Search Documents

By Paul L. Horrer

Costly damage by severe wave attack to many engineering structures has illustrated the need for a consideration of the nature of wave action in plans for offshore drilling operations. Using wave data it is possible to answer questions pertaining to engineering problems such as platform elevation, structure orientation, and expected wave forces. For locations where wave records are not available a technique can be used to obtain information about wave characteristics from past meteorological data and near shore submarine topography. Forces exerted on structures by waves may be divided into four parts. A completed study is given in which frequencies of various wave heights and maximum frictional drag forces are computed for a typical offshore drilling site. INTRODUCTION Waves of tremendous proportions accompanying hurricane winds crash against breakwaters and other offshore structures causing untold damages. Wave forces exerted on structures at these times are enormous, as shown by past records of incidents where massive portions of breakwaters have been broken off and moved by waves. On other similar occasions, whole structure; have been unloosed and smashed or floated away. These incidents, which seem almost incredible, serve to illustrate the great amount of energy contained in large waves, and to show that this energy results in powerful forces destructive to offshore installation~ which are not designed sufficiently strong to withstand wave attack. In the past the expected frequencies of waves having various characteristic.% have rarely been considered in the design of structure affected by wave action. As a result, many structures have failed to accomplish the purpose for which they were designed or have collapsed under wave attack. Others have been constructed to withstand greater wave energy than is ever encountered, with resulting waste of material and construction time. In this study an analysis is made of the frequencies of waves having different characteristics which affect the plans for offshore drilling installations. After such an analysis the erection of these structures can proceed with less risk involved and with more efficiency and economy. ENGINEERING ASPECTS In the offshore drilling program wave forces play an extremely important part in design and construction of drilling rigs in shallow water. The design of a platform or other structure from which drilling equipment is operated is critical, becauze any damage to the platform may endanger personnel and result in complete loss of equipment. Since a platform built too close to the water would be battered by breakers, and one built unnecessarily high would involve undue expense, it is necessary to know the most desirable elevation at which the platform should be erected. This is only one of many questions about structural planning which can be answered using existing technique for determining wave characteristics. The purpose of efficient design for the portions of many types of offshore structures which are acted upon by wave forces is the same as that of all designs which deal with frictional forces of a fluid on a solid. For these structures the problem is comparable to that encountered by undersea craft moving through water, except that in the case of a fixed structure the force is produced by the water moving past the model. For off shore sructures which are extremely rigid the frictional forces may be nearly negligible compared with the impact or shock forces imparted by breaking waves. In all case; the better design is that which offers the least resistance to the opposing forces. From a consideration of wave forces, each drilling structure varies in efficiency depending upon the type and amount of superstructure in contact with the waves. For example, round piling and bracing offer less resistance to wave forces than do I-shaped ones. All network superstructure such as cross bracing should be kept to a minimum and at as low an elevation as possible, so that it will not expecience the pressure exerted at the tops of breaking waves. Models of proposed structures can be tested in wave tanks and in the field to ascertain the efficiency of specific designs. Past experience in beach and shoreline engineering has shown that, although changes in the topography of the bottom very near shore do not seem to be occurring, the natural forces involved may be in a delicate balance such that a static state exists. Interruptions of any of these natural forces by erecting offshore structures are likely to cause undesirable effects. Changes in beach profile result partly from sediment being brought into suspension by the orbital motion of waves and partly from the transport of sediment by longshore currents. With the erection of an offshore structure and consequent change in the combined effects of these two forces, unfavorable deposition upon, or erosion of, the bottom at the site may occur. Therefore, combination wave and current studies are essential for the solution of problems involved in the design of most marine structures. TECHNIQUE FOR OBTAINING WAVE INFORMATION In determining the probable effect of wave action on an offshore drilling structure, it is first necessary to know the usual frequencies of certain wave types for the given location. A technique has been developed which provides a means for obtaining information about wave characteristics in the

Jan 1, 1949

By Paul L. Horrer

Costly damage by severe wave attack to many engineering structures has illustrated the need for a consideration of the nature of wave action in plans for offshore drilling operations. Using wave data it is possible to answer questions pertaining to engineering problems such as platform elevation, structure orientation, and expected wave forces. For locations where wave records are not available a technique can be used to obtain information about wave characteristics from past meteorological data and near shore submarine topography. Forces exerted on structures by waves may be divided into four parts. A completed study is given in which frequencies of various wave heights and maximum frictional drag forces are computed for a typical offshore drilling site. INTRODUCTION Waves of tremendous proportions accompanying hurricane winds crash against breakwaters and other offshore structures causing untold damages. Wave forces exerted on structures at these times are enormous, as shown by past records of incidents where massive portions of breakwaters have been broken off and moved by waves. On other similar occasions, whole structure; have been unloosed and smashed or floated away. These incidents, which seem almost incredible, serve to illustrate the great amount of energy contained in large waves, and to show that this energy results in powerful forces destructive to offshore installation~ which are not designed sufficiently strong to withstand wave attack. In the past the expected frequencies of waves having various characteristic.% have rarely been considered in the design of structure affected by wave action. As a result, many structures have failed to accomplish the purpose for which they were designed or have collapsed under wave attack. Others have been constructed to withstand greater wave energy than is ever encountered, with resulting waste of material and construction time. In this study an analysis is made of the frequencies of waves having different characteristics which affect the plans for offshore drilling installations. After such an analysis the erection of these structures can proceed with less risk involved and with more efficiency and economy. ENGINEERING ASPECTS In the offshore drilling program wave forces play an extremely important part in design and construction of drilling rigs in shallow water. The design of a platform or other structure from which drilling equipment is operated is critical, becauze any damage to the platform may endanger personnel and result in complete loss of equipment. Since a platform built too close to the water would be battered by breakers, and one built unnecessarily high would involve undue expense, it is necessary to know the most desirable elevation at which the platform should be erected. This is only one of many questions about structural planning which can be answered using existing technique for determining wave characteristics. The purpose of efficient design for the portions of many types of offshore structures which are acted upon by wave forces is the same as that of all designs which deal with frictional forces of a fluid on a solid. For these structures the problem is comparable to that encountered by undersea craft moving through water, except that in the case of a fixed structure the force is produced by the water moving past the model. For off shore sructures which are extremely rigid the frictional forces may be nearly negligible compared with the impact or shock forces imparted by breaking waves. In all case; the better design is that which offers the least resistance to the opposing forces. From a consideration of wave forces, each drilling structure varies in efficiency depending upon the type and amount of superstructure in contact with the waves. For example, round piling and bracing offer less resistance to wave forces than do I-shaped ones. All network superstructure such as cross bracing should be kept to a minimum and at as low an elevation as possible, so that it will not expecience the pressure exerted at the tops of breaking waves. Models of proposed structures can be tested in wave tanks and in the field to ascertain the efficiency of specific designs. Past experience in beach and shoreline engineering has shown that, although changes in the topography of the bottom very near shore do not seem to be occurring, the natural forces involved may be in a delicate balance such that a static state exists. Interruptions of any of these natural forces by erecting offshore structures are likely to cause undesirable effects. Changes in beach profile result partly from sediment being brought into suspension by the orbital motion of waves and partly from the transport of sediment by longshore currents. With the erection of an offshore structure and consequent change in the combined effects of these two forces, unfavorable deposition upon, or erosion of, the bottom at the site may occur. Therefore, combination wave and current studies are essential for the solution of problems involved in the design of most marine structures. TECHNIQUE FOR OBTAINING WAVE INFORMATION In determining the probable effect of wave action on an offshore drilling structure, it is first necessary to know the usual frequencies of certain wave types for the given location. A technique has been developed which provides a means for obtaining information about wave characteristics in the

Jan 1, 1949

By Frederick Prime

In this supplementary list no titles to which an * is prefixed have been seen by the compiler; and he will be most thankfu1 to have any omissions or inaccuracies in the list sent to him to be published as a second supplement in the next volume of the Transactions. The author is indebted to Messrs. Robert Clarke, of Cincinnati; Thomas Macfarland, of Towanda; Professor F. W. Simonds, of Chapel Hill; and Professor J. J. Stevenson, of New York, for valuable assistance. Cedar Point IRON Company, Baltimore, July 31st, 1880. Alabama. Geological Survey of Alabama. Report of Progress for 1877 and 1878; by Eugene A. Smith, State Geologist. Montgomery, 1879. 8vo., 139 pp., and 4 maps.

Jan 1, 1880

By Haydn H. Murray, Sam H. Patterson

The term "clay" is somewhat ambiguous un¬less specifically defined, because it is used in three ways: (1) as a diverse group of fine-¬grained minerals, (2) as a rock term, and (3) as a particle-size term. Actually, most persons using the term "clay" realize that it has several meanings, and in most instances they define it. As a rock term, clay is difficult to define be¬cause of the wide variety of materials that com¬pose it; therefore, the definition must be gen¬eral. Clay is a natural earthy, fine-grained ma¬terial composed largely of a group of crystalline minerals known as the clay minerals. These minerals are hydrous silicates composed mainly of silica, alumina, and water. Several of these minerals also contain appreciable quantities of iron, alkalies, and alkaline earths. Many defini¬tions state that a clay is plastic when wet. Most clay materials do have this property, but some clays are not plastic; for example, halloysite and flint clay. As a particle-size term, clay is used for the category that includes the smallest particles. The maximum-size particles in the clay-size grade are defined differently on various grade scales, Soil investigators and mineralogists gen¬erally use 2 micrometers as the maximum size, whereas the widely used scale by Wentworth (1922) defines clay as material finer than ap¬proximately 4 micrometers. Some authorities find it convenient to use the term "clay" for any fine-grained, natural, earthy, argillaceous material (Grim, 1968). When used this way, the term includes clay, shale, or ar¬gillite, and some argillaceous soils. Even though no standard definition of the term clay is accepted by geologists, agronomists, engineers, and others, the term is generally un¬derstood by those who use it. Clay is an abun¬dant natural raw material, and it has an amaz¬ing variety of uses and properties which will be discussed in this chapter. Clays rank among the leading industrial min¬erals in both tonnages produced and total value. Their importance is indicated in Table 1, which lists the 1970, 1971, and 1972 production and values according to the U.S. Bureau of Mines (Ampian, 1972). Adequate reliable statistical data on which to summarize world production of clay are un¬available; this paragraph outlines the world re¬quirements for clay only in a very general way. According to one estimate, the world bentonite production in 1972 was 3.5 million tons (Anon., 1973a), but in the authors' opinion it was prob¬ably at least 5 million tons. The total fuller's earth produced was at least 1.5 million tons and may have been as much as 2 million tons. The total world kaolin production in 1972 was more than 10 million tons. Approximately 7 million tons of this total was produced in only two regions-the Georgia-South Carolina kaolin belt in the United States and the Cornwall re¬gion, United Kingdom. The world's 1972 out¬put of ball clay, which is also produced pri¬marily in the United States and the United Kingdom, was approximately 1.5 million tons or perhaps a little more. The total world fire clay production in 1972 was probably about one and one-half to two times and the miscellaneous clay production three times the United States production. As industrial minerals, clays are a complex group that consists of several mineral commodi¬ties, each having somewhat different mineral¬ogy, geologic occurrence, technology, and uses. In this chapter these commodities are organized

Jan 1, 1975

By Arthur Notman

YEAR ago, the Committee on Mineral Economics ventured to predict a more realistic attitude by the public toward the folly of seeking to have more by making less under the guidance of the Blue Eagle. A unanimous decision of the Supreme Court of the United States has now laid that embattled bird to rest. De rnortuis nil nisi bonum. In spite of dire predictions of disaster to follow its early demise, the metal industries and many others have improved substantially. One could name many indications of that improvement, and on the strength of stock-market activities might assume

Jan 1, 1936

Gentlemen.-The Institute was founded 54 years ago "with the object of promoting the arts and sciences connected with the economic production of the useful minerals and metals and the welfare of those employed in these industries by means of meetings for social intercourse and the reading and discussion of professional papers, and to circulate by means of publications among its members and associates the information thus obtained," At least once a year it is well to take stock of our assets, review our performance and determine how well we are now carrying out the purposes of our Founders. There can be no question as to the work the Institute has done and is doing in promoting the arts and sciences in the fields of mining and metallurgy. One needs only to contrast the methods, the labor and the costs of a half century ago with those now to visualize how far we have gone in the development of accurate technology and sound economics in mineral and metal production. The great mines, mills and smelters of the present, handling individually thousands of tons per day, would' have been impossible except for the accumulation of knowledge, the development of theory, and the improvement in practice that has characterized the period since the foundation of the Institute. The United States has prospered in the last half century greatly, and this has been due not merely to the possession of great natural resources, but to these resources being reduced to possession and put to work. The absence of customs barriers and the freedom of trade across the whole width of this great continent has been an important factor in the growth of our wealth. Unrestricted interchange of goods has permitted each citizen to draw on the resources of the whole country. However, these are but subsidiary causes of prosperity. The free interchange of scientific and technical data, by making the whole body of facts and theory available to each worker, has made this quick and unrivaled development possible. In promoting this free trade in knowledge the Institute may claim a large place without fear of denial. The .72 volumes of TRANSACTIONS, the special volumes, the bulletins and the other publications that have been issued, include a store of knowledge of the arts and sciences related to the production and use of metals and minerals not duplicated elsewhere. The large list of foreign members-1746 in number-few of whom ever have opportunity to attend meetings and all of whom derive their main benefits from membership through the pub-

Jan 1, 1928

By Richard L. Ashbrook, John F. Wallace

Several high-temperature eutectics of cobalt and nickel alloys were modified by small additions of selected elements. Thes-e alloys were compared to unmodified melts for microstructural variations. A few modified compositions were selected on the basis of structure and their tensile and stress-rupture behavior determined. The results of stress-rupture tests in air at 1800 F and room-temperature tensile tests of four high-temperature eutectics showed modification capable of producing substantial improvements in properties. The microstructures were altered and mechanical properties improved by: a.) dispersing a subordinate phase more uniformly throughout the matrix; b) replacing large continuous -network or platelike constituents with small equiaxed discontinuous phases; and c) by forming new, finely divided phases. tHE term "modification" is most commonly used to describe the refinement in microstructure of the Al-Si eutectic that occurs as a result of rapid cooling from the melt or on slow cooling after treatment with small amounts of sodium.1 "Modification" has also been used to describe the change from flake to spheroidal graphite in the austenite-graphite eutectic of cast iron.2 This change of graphite shape is accomplished by small additions of cerium or magnesium.3 Other systems have also been shown to be capable of modification, for example: Pb-Sn by copper;4 Al-Cu by sodium;5 Al-Mn by sodium;5 and Pb-Sb by aluminum.5 Although modification of Al-Si alloys and cast irons is usually accompanied by improved mechanical properties, a general definition of modification has been suggested to include the effect of small quantities of impurity elements on the microstructures of all eutectic alloys, regardless of the effect on the mechanical properties.6 In this paper, the term "modification" is employed in a broad sense to include the formation of third phases or even the supplanting of one of the binary eutectic phases by a third phase. The mechanism of modification, as for any solidification phenomenon, must be considered primarily in terms of nucleation and growth. Although both nuclea-tion and growth mechanisms are required to explain all the phenomena observed in connection with the solidification of modified eutectics, various investigators have usually favored one or the other.7"16 It has been shown that modification of a binary eutectic can be effected by addition of a solute element that has greatly different distribution coefficients or k values in the two phases of the eutectic. Under these conditions, differences in the temperatures at the solid-liquid interfaces of the two phases retard the growth of one phase with respect to the other.4 It has also been shown that increased undercooling favors a transition from a rodlike eutectic to a globular eutectic.17 A mechanism proposed for the transition from lamellar to rodlike eutectics depends on the concept of constitutional super cooling.18 The modification of eutectic alloys may be of interest for high-temperature service as well as at room temperature. Although "high-temperature eutectic alloys" may appear to be a contradiction in terms, many eutectic systems, including those studied in this work, have melting points in excess of 2400°F. One of the mechanisms by which high-temperature alloys are strengthened is dispersion of a relatively brittle phase such as an oxide, carbide, or an inter-metallic compound throughout a ductile matrix. For a given volume fraction of dispersed phase, strength is increased by decreasing the size and spacing of the dispersed particles.19'20 Furthermore, room-temperature ductility may also be increased by changing the shape of a brittle dispersed phase from platelike to equiaxed or spheroidal.8 Overaging and redissolving of the secondary phase limit the maximum temperature to which precipitation-hardened alloys can be used. However, in a binary eutectic system, both phases coexist up to the melting point. Although all eutectic structures are not completely stable,21 a dispersion-hardened cast high-temperature alloy might result if a fine distribution of one of the eutectic phases could be obtained during solidification. An additional reason for interest in eutectic alloys is their excellent castability.22 Since eutectic alloys, like pure metals, freeze at a single temperature rather than over a range of temperatures, their castability is superior to solid-solution alloys with long liquidus to solidus ranges. The purpose of this research was to study the effects of small solute additions on the microstructure and mechanical properties of a number of high-melting-point eutectic compositions.

Jan 1, 1967

The Role of the Drilling Contractor BY FERRIS E. SAINSBURY Ron Haxby, Occidental Minerals What is the best method for drilling a 12-in. diam hole to a depth of 1200 ft and maintaining the deflection within 25ft from vertical? Ferris Sainsbury: In order to drill a 12-111. hole down to 1200 ft, In most places you would have to employ a rotary tricone bit With a down-the-hole hammer, I expect by that depth significant Inflows of water would be experienced Even with foams, we would not be able to get the water out of a hole of that diameter So the down-the-hole tricone method of drilling would be best. To keep it straight, we would probably employ the largest square drill stem compatible with the diameter of the hole. Ron Haxby: Is it common in drilling contracts to put in a vertical hole clause? Ferris Sainsbury: You can put in the vertical hole clause Ron Haxby: Does it cost more? Ferris Sainsbury: Normally, if the hole deviates, the driller can correct it with deflection wedges and will charge it back to you at cost, plus 10% or somewhere along that range Any drill hole has a tendency to go perpendicular to the dip, and there are times when stabilization systems are not successful in preventing the hole from turning into the dip of the formation. The only solution, in this situation, is to go in with an oriented wedge and kick the hole back out.

Jan 1, 1979

A completely automated primary crusher is now in operation at Kaiser Steel Corp.'s Eagle Mountain, Calif., iron mine. The word "completely" is italicized to underscore its literal meaning- automation so thorough that even the control room for the crusher does not require a man to watch the flickering dials and lights. The automation of the unit is such that its operation, including starting and stopping, are controlled from the secondary crusher station. The crusher-a Symons 60-in. gyratory which can handle 3600 tph-features built-in safety devices that will turn the crusher off if oil pressure drops, if oil overheats, if bearing temperatures exceed permissible limits, or if parts of its electronic brain fail. According to reports, the worst that can now happen is a plugging of the crusher.

Jan 6, 1963

By C. K. Leith

1 apologize for attempting to talk in a field in which 1 am by no means a specialist, but some of the problems brought up have much in common with other minerals. It touches the field in which we are all interested and it is a field in which our Mineral Inquiry has been giving special attention during the last two years. While it is the primary business, of course, of this Institute to consider the physical facts and technology of minerals, we now face the necessity of considering the minerd industry in its broader economic, social, and political relationships. We have run into a traffic jam—as though a load of hay had been spilled on the road. It makes no difference whether we are drivers or passengers, technical or nontechnical men, we have to get the load off the road before we can go farther. We are conscious of very many difficulties which are outside of the ordinary range of cost accounting or methods of mining or the usual thing with which we concern ourselves. We have extensive readjustments to make in our social and economic and political contacts. It is up to us to find out what is the matter. As a matter of fact, we do not know what is the matter in any comprehensive way. We have many suggestions as to difficulties here and there. Many people are working on the problem, but when the mineral industry as a whole is asked what is a reasonable course of procedure, what is its program, what would be a reasonable state or national policy, I think you will agree with me that we have no spokesman able to outline even a semblance of such a general policy. We sit back and criticize when somebody else steps in, as Governor Murray stepped in, and as many others of our state governors and legislators are stepping in, to do things which we do not think are reasonable. When they say, "What is a reasonable program? " we find ourselves caught napping. We have not agreed on a program. The other day in talking with one of the leaders of the western radical movement, I was twitting him on having no sound and comprehensive conservation program. He said, "What is yours, and what is the program of the mineral

Jan 1, 1932

By Theodore H. Eyde

In the southwest porphyry copper province, the virgin prospect with good copper mineralization cropping out has disappeared. Future discoveries will require an increasingly sophisticated arsenal of exploration techniques and concepts. One of the latter, stratigraphic analysis, is a technique which is often overlooked. A surprising number of exploration geologists still think of porphyry copper deposits as occurring wholly within intrusive bodies such as quartz monzonite or granodiorite. Disseminated copper mineralization, though genetically related to intrusive rocks, can occur within both the intrusive and the intruded rocks. At present, as much as 30% of the total copper produced from disseminated copper deposits in the Southwest originate from the intruded rocks rather than the intrusive.

Jan 4, 1972

By R. L. Sebastian

ALUMINUM'S war history is the record of a successful race to expand facilities fast enough to meet the multiple increases in military requirements, principally for aircraft. From the beginning of the war program in 1940 through 1942, requirements estimates were repeatedly lifted to new high levels, and plans for increasing capacity had to be constantly revised. In 1943, basic metal supply caught up with and exceeded requirements, and by 1944, the surplus of primary production was large enough to force reduction in output and plant closings. In the past two years, ingot capacity has been ample, though periodic critical shortages have been experienced for a few fabricated shapes as a result of sudden shifts in demand. And now with all controls lifted we are faced with surplus capacity, surplus stocks, and surplus scrap. In 1938 the Aluminum Co. of America was the only U. S. producer of primary

Jan 1, 1946

By LIONEL E. BOOTH

ORE tests are made for the purpose of determining the correct methods of treatment for any particular ore. They should be conducted so as to insure that the results obtained in actual mill practice, on ore of similar grade and physical nature, will duplicate the results obtained in the test work. As the expenditure of many thousand of dollars may be involved in the building of the necessary mill, the testing of ores calls for extreme care and skill in handling laboratory machines, and a knowledge of actual practice to guard against the danger of obtaining results in test work that would be impractical to duplicate on a commercial scale. The importance of a correct sample of the ore is at once apparent. No matter with what degree of care the test 4rk is done, it loses its value when made on an unrepresentative sample. It is the first safeguard against future disappointments in the loss of capital and time. A number of failures in the past have been traced directly to faulty or lax methods in obtaining the ore sample.

Jan 1, 1924

The fundamentals of blasting involve both the properties of explosives and of the rock being blasted. Four of the most important explosive properties appear to be energy density, bulk density, rate of energy release and the pressure- time history of the gases produced. Important rock properties are density and porosity, strength, and energy absorption including the effective moduli of elasticity. Rock structure also has a marked effect on its properties: for example, joints, bedding, and fracture alteration. Several mechanisms enter into rock fragmentation by blasting. These include slabbing, radial fracturing, crushing and bursting by the gas bubble. All of these factors are closely related to properties of both explosives and rock. Slabbing depends upon the first generated stress wave, whose shape and magnitude are a result of the pressure generated by the explosive, its time history and the resultant response of the rock, including its ability to sustain the stress wave. Actual slabbing, in turn, is a function of the magnitude and shape of the pressure pulse and the tensile strength of rock. Further fragmentation depends to a great extent upon the amount of gas in the bubble and its energy and pressure.

Jan 10, 1967

By Lysle E. Shaffer

INCREASING attention has been given in the last decade to the possibilities of mine leasing in the West. The practice as described in this article does not refer to the leasing of entire properties for corporate operation. It is intended to deal rather with the advantages and problems incident to leasing portions of properties to individuals who themselves, individually or in groups, do the actual mining and transportation of the ore. These individuals are sometimes called "leasers" and sometimes called "tributors." The contracts under which they work set up an independent relationship of lessor and leaser, between themselves and the mineowner or operator. This relationship has many advantages to both sides over those created by the ordinary relationship of employer and employe. From the standpoint of the owners there is no liability on independent contractors for industrial injuries, social security taxes, unemployment taxes, or the manifold restrictions of the Federal Labor Relations and Wage Hour Acts and similar state acts where they exist. As the leaser's income depends on the quantity and quality of ore produced, there is a distinct incentive for maximum production of a good grade of ore. This in turn promotes careful mining of the areas under lease. Ordinarily in mining, labor cost is a high percentage of the total cost of operation. Under a leasing system, even if the leasers be allowed to retain half of the gross values that they produce, and the owner or operator gets half, in the case of marginal ore bodies this is ordinarily more than the lessor would realize if the property were worked by day labor. In some instances mineral deposits under a leasing system may become ore, whereas under a day-labor system they would

Jan 1, 1948

By William P. Blake

(Canal Zone Meeting, November, 1910.) A DEPOSIT of manganese-ore near Tucson, Ariz., merits notice by reason of the peculiar form in which it occurs, and as a striking. example of ore-deposition by vadose upward capillary flow of metal-bearing solutions with concentration at the surface of the country-rock. This deposit occurs at the northern end of the Coyote mountains, about 40 miles west of Tucson, upon the outcropping beds of porphyritic rock, which appear to be partly-metamorphosed strata of volcanic tufa, probably of late Secondary or of Tertiary age. The strata dip northward at a low angle, and present a series of basset-edges in parallel lines of outcrop, east and west, facing the south and extending over many acres. Successive groups of these outcrops, from 5 to 20 ft. in breadth, are coated with oxides of manganese in lustrous black films and crusts, shining in the sunlight like polished ebony, and covering the whole surface of the rock above the soil. Seen at a little distance, these croppings look like solid ledges of massive and pure ore; but closer inspection and a few blows of the hammer reveal their true nature as a superficial coating allied in origin to the blackened shining surface of rocks exposed in desert-regions, familiarly known as " desert paint" or "desert varnish,"' similar to the phenomena described by me in a former paper, but much thicker and heavier. * By reason of the death of the distinguished author, this communication, probably his last communication to technical literature, is published without revision of the proofs by him. A term first given y G. K. Gilbert. See Rocks, Rock-Weathering, and Soil; by George P. Merrill, p. 256 (New York, 1897). Superficial Blackening and Discoloration of Rocks, Especially in Desert Regions, Trans., xxxv., 371 (1905).

Sep 1, 1910

By W. B. Plank

The figures on enrollment in the engineering schools of the United States and Canada indicate that the total number of students in these schools for the current year, 1949-50, is about 10% less than it was a year ago. This year, 226,533 undergraduates and graduate students are studying engineering in the United States and Canada as compared with 249,913 students last year. These figures are taken from advance data in the Journal of Engineering Education for February 1950.

Jan 5, 1950

At its meeting on February 21, 1933, the Board of Directors passed the following resolution defining and expressing the policy of the Institute with respect to official participation or action in controversial matters: WHEREAS, the Board of Directors at its last meeting passed the following resolution : "The Board of Directors, having been appealed to by several Local Sections for advice concerning the attitude and policy of the Institute relating to the endorsement of candidates for public office, the following statement of policy is formulated: "Whereas, the American Institute of Miming and Metallurgical Engineers is organized for purely professional and scientific purposes, and whereas diversity of opinion among its members on partisan or political questions is inevitable, it is the ex- pressed policy of the Institute to refrain from official participation or action in political and semi-political matters."

Jan 1, 1946

By Leo Greenberg

As one of its functions, the U.S. Bureau of Mines gathers and analyzes mine accident data, and then publishes annual reports on work injury experience in the various segments of the minerals industry- coal, nonmetals, rock. These reports contain a wealth of detailed data, with a multitude of analyses and cross-tabulations, all intended to shed as much light as possible on accidents and to suggest possible ways of reducing them. In this article, the terms, "injury" and "accident" will at times be used interchangeably to denote accidents which cause disabling injury. The Bureau bases many of its analyses on American National Standard Z16.1 for recording and measuring work injury data. This document establishes two models for measuring disabling injury experience: (1) the frequency rate, obtained by dividing the number of man hours into the number of injuries multiplied by 1 million, and (2) the severity rate, similarly constructed, with the variable of interest being the number of days lost due to these injuries. Similar computations are performed by the U.S. Bureau of Labor Statistics and the National Safety Council. Additionally, these models are used in many other countries, sometimes with minor changes.

Jan 1, 1971

We have seen that the first coal development in Pennsylvania was in the Pittsburgh bed in the southwestern corner of the state. The next mining, in point of time, was done in Clearfield County along the West Branch of the Susquehanna River, but the amount of mining done was quite small for a number of years and was soon exceeded by that from the area north of the Susquehanna River in Tioga, Bradford and Lycoming Counties, which will be considered now. It is claimed that coal was first noticed in Tioga County, in 1792, by Robert and Benjamin Patterson who were leading a party of settlers from Williamsport to southern New York, and while clearing a road near the site of Blossburg, found coal, which was said to be good. About 1815 David Clemons made an arrangement with Aaron Bloss, owner of the land, to work some of the coal and hauled the first load down the river to Painted Post, N. Y., as there were no available markets in his own state. Smiths found it an excellent fuel and apparently he found a ready market for the small amount he could transport by wagons and sleighs. As wood began to become scarce around the towns in New York State, the knowledge of the coal deposits in the mountains at the head of the Tioga River attracted attention to the field and the necessity, for means of transportation from it. Some coal had been floated down the river, but navigation was uncertain and dangerous. In 1827 an iron plant was built, and to ship its product and coal, it was proposed to build a canal along the river to reach Corning, N. Y. A company had been chartered in 1826 in Pennsylvania to "make a navigable canal or slack-water navigation" to the state line and coal was shipped on rafts of logs, both being sold, during highwater. In 1828 the company was authorized to build a railroad instead of a canal, and in September 1840, the railroad was completed from Corning to Blossburg.1 That some coal from Pennsylvania had been reaching southern New York towns prior to the improved means of transport is shown by the report of a committee to the New York Assembly: "the bituminous coal has been brought to us either from Great Britain or from that part of our own country which borders on, and lies west and south of the Susquehan-

Jan 1, 1942