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By O. Jantti, Erkki Laurila, R. T. Hukki

INVESTIGATION of the methods of analyses for magnetite and ilmenite in the Otanmaki iron-titanium ore and respective mill products has resulted in certain improvements in the methods conventionally employed. The outcome of the investigations is summarized as follows: 1—Development of a diamond-drill core analyser for the determination of magnetic susceptibility of drill cores containing magnetic minerals. 2—Development of a magnetite-ilmenite analyser for pulverized products. 3—Development of a potentiometric method of chemical analysis for the determination of iron, vanadium, and titanium in succeeding steps from one test sample. 4—Proposal for a continuous and automatic magnetite assay method. Diamond-Drill Core Analyser The conventional method of assaying diamond-drill cores consists of splitting the cores, pulverizing them and running chemical analyses on representative samples. The physical properties of magnetic minerals, however, offer an entirely different approach to obtain similar final result by the measurement of respective magnetic susceptibilities in a properly designed instrument. This instrument is shown in Fig. 1. Essentially it consists of a magnetic unit, A, and of a meter unit, B. On top of A is a slot where a piece of diamond-drill core C is visible. The magnitude of disturbance in the original magnetic field caused by the magnetic minerals in the drill core can be observed from the microammeter. This reading is a function of the combined susceptibilities of all magnetic grains in the magnetic field. The magnetic unit is built of E-sheets of a shell transformer, as shown in Fig. 2. The primary coil and two identical secondary coils are wound around the central leg and end legs, respectively. The drill core under examination is placed into one of the air gaps as shown in Fig. 2. The number of ampere-turns of primary coil excited by 50 or 60-cycle ac give a maximum induction of about 600 gauss in the air gaps. The secondary coils are connected in series in the opposite direction. Thus their voltages compensate each other if no drill core exists in the air gap or if the susceptibility of the drill core is equal to zero. As soon as the susceptibility becomes greater than zero, the balance of the magnetic circuit is disturbed, resulting in increased voltage in the terminals of coil 1 and in a respective decrease of voltage in the terminals of coil 2. The voltage difference thus produced is a function of the effective susceptibility of the drill core. If the magnetic grains in the drill core are unevenly distributed, the voltage difference varies as the core is rotated around its own axis. The voltage difference is measured with a Bren-tan0 tube voltmeter. If extreme sensitiveness is desired, the established symmetry of the magnetic circuit does not allow reduction of the 0-voltage difference far enough. Therefore a compensatory voltage of a correct phase taken from the terminals

Jan 1, 1952

By V.F. Marsters

Seepages of oil in Ecuador have been known for many years. The locality first to receive attention, and still worked in a modest way, lies on the north shore of the Santa Elena peninsula, between La Puntilla and Salinas. Operations mere first conducted largely by local cdpital. Later, foreign companies acquired large blocks of land, where they have done considerable drilling. For details concerning present drilling activities in Ecuador, we are indebted to Leon Price, an Ame~ican resident engineer of Ecuador. The information solicited came to the author through the office of the American Consulatell with permission to use it. The coastal plain bordering the Province of Tumbes, Peru, continues to the northeast, but narrow on passing the Zarumilla River. From this point northward it widens toward Santa Rosa. In fact, the pampas, as shown on the official Wolf map, correspond fairly well to the areal extent of tbe coastal plain as far as Guayaquil. This is shown in a general way on the accompanying map. The author understands that the Guayaquil enlbayment is bordered on all sides by the coastal plain, as recognized at Tumbes and farther southwest, and that it can be followed without a break as far north as Palmar. This view is supported by the mapped area regarded by Mr. Price as favorable or possible oil territory. Moreover the islands in the Gulf of Guayaquil are the same geologically as the coastal edge, being composed of Tertiary sediments. The author understands also that Tertiary formations occur north of Palmar. According to a report by Mr. Cardon, of Guayaquil, Tertiary sediments are exposed in the region of San Francisco and extend to and beyond Pta. Calera. There is also reason to believe that at least the lower part of the valley of the Santiago River is occupied by Tertiary sediments, ~~hich probably border the const line and extend into the River Mini l)nsin, and into Colombia. On the south coast there are many seepages, most of them near the inner edge of the coastal plain, between Zarumilla and Santa Rosa and also between Santa Rosa and Machala. I11 the latter region are

Jan 1, 1923

By V. F. Marsters

Seepages of oil in Ecuador have been known for many years. The locality first to receive attention, and still worked in a modest way, lies on the north shore of the Santa Elena peninsula, between La Puntilla and Salinas. Operations mere first conducted largely by local cdpital. Later, foreign companies acquired large blocks of land, where they have done considerable drilling. For details concerning present drilling activities in Ecuador, we are indebted to Leon Price, an Ame~ican resident engineer of Ecuador. The information solicited came to the author through the office of the American Consulatell with permission to use it. The coastal plain bordering the Province of Tumbes, Peru, continues to the northeast, but narrow on passing the Zarumilla River. From this point northward it widens toward Santa Rosa. In fact, the pampas, as shown on the official Wolf map, correspond fairly well to the areal extent of tbe coastal plain as far as Guayaquil. This is shown in a general way on the accompanying map. The author understands that the Guayaquil enlbayment is bordered on all sides by the coastal plain, as recognized at Tumbes and farther southwest, and that it can be followed without a break as far north as Palmar. This view is supported by the mapped area regarded by Mr. Price as favorable or possible oil territory. Moreover the islands in the Gulf of Guayaquil are the same geologically as the coastal edge, being composed of Tertiary sediments. The author understands also that Tertiary formations occur north of Palmar. According to a report by Mr. Cardon, of Guayaquil, Tertiary sediments are exposed in the region of San Francisco and extend to and beyond Pta. Calera. There is also reason to believe that at least the lower part of the valley of the Santiago River is occupied by Tertiary sediments, ~~hich probably border the const line and extend into the River Mini l)nsin, and into Colombia. On the south coast there are many seepages, most of them near the inner edge of the coastal plain, between Zarumilla and Santa Rosa and also between Santa Rosa and Machala. I11 the latter region are

Jan 1, 1923

By Jerry R. Johanson

The practical application of rolling theory to the design of roll presses is reviewed along with aspects of plant operations which must be considered to produce the required product economically. Appropriate parameters to scale up from laboratory tests to full- scale press operation and improvements possible in existing operations are discussed.

Jan 1, 1977

By Richard Miller

RECENT studies of creep have made it apparent that plastic deforma-tion may occur in metals under stresses less than the elastic limit as deter-mined from short-time tests. In summarizing conclusions drawn from creep tests by various investigators, Tapsell1 said: "It is evident that if a material has a true elastic range, the elastic limit must represent the maximum stress for no creep." The presence of a. definite elastic limit, represented in single crystals by a critical or threshold shearing stress, is claimed by Schmid2, Elam3 and others who have investigated the plastic deformation of single crystals. However, this "law of critical shearing stress" was deter-mined2 from short-time tests, and the measurement of the deformation was made with apparatus primarily designed to observe large amounts of plastic deformation, not to detect elastic changes. Experimental data recently obtained with highly sensitive instru-ments by A. W. Hanson4 on zinc and by Podaschowsky5 on rock salt indicate that the elastic range in single crystals is considerably narrower than formerly was supposed. Moreover, a theoretical possibility of permanent deformation, under the influence of even the smallest shear stress in single crystals above a certain temperature (Td), has been developed by G. I. Taylor6. This evidence seemed to warrant an examination of the elastic limit in large single crystals by means of creep tests. The first metal chosen for examination was zinc.

Jan 1, 1936

By J. T., Norton

As cold working is an important feature in a great many of the fabricating processes now applied, this paper presents some ideas on the nature and results of the plastic deformation produced in this operation. The art of manufacturing metal for practical uses is very old and has undergone very great development. The science of metals has- also developed very rapidly recently and the various processes to which metals are submitted are much better understood now than they were even a short time ago. All the knowledge that can be obtained on this subject is useful because it promotes efficiency in converting metal into finished articles.

Jan 1, 1927

By K. R. Waugh, Barbara S. Brown, D. W. James

AN electronic data-processing system is described which permits rapid, accurate, low-cost processing of strain-dependent damping data utilizing equipment normally available within the service facilities of most large laboratories. On analyzing the record of a stress-dependent damping test, the operator usually measures the double amplitudes at several points on the decay curve. The logarithmic decrement is then calculated for decay between consecutive amplitudes. These values of 6 are plotted against the corresponding maximum surface shear stress, T, which is proportional to the average of the two amplitudes between which is calculated: where d is the specimen diameter. The period of the vibration is not necessarily constant during decay; thus, each cycle must be counted. A decay curve may extend to, perhaps, 1000 cycles, and at least two curves are always obtained for each specimen or set of conditions. It can, therefore, be seen that manual analysis of decay curves is both tedious and costly in terms of man-hours. Furthermore, the resolution of the record is often such that accurate measurement of amplitude is extremely dif-

Jan 1, 1969

By R. E. Sabaski

Total grinding mill system life is dependent upon the original selections and specifications of its components: the mill, its drive, drive motor, motor control, and power system. This paper discusses the complex considerations involved and the critical decisions which must be made by the buyer, the mill manufacturer, and by the gear vendor during the proposal and ordering stages. Interrelations between the mill manufacturer and the gear vendor, application of ACMA standards, how drive standards and specifications are refined through steady-state and computer-simulated torsional analyses are included, along with correlational field testing, as demands for larger sizes challenge the current state of the art.

Jan 1, 1984

By George E. Roberts

The maintenance of the common gold standard is the most important cooperative undertaking in the world. The war broke up this relationship and brought about a state of great disorder in the currencies and exchanges. After the war the countries all began to grope their way back to the gold standard as the best means of establishing trade and financial relations with each other. With this movement began a general decline in commodity prices. The question has been raised whether the world's return to the gold standard was not forcing prices back to the prewar level. Also, the question is raised whether the world has not outgrown the supply of gold as the basis of credit. Because Europe readjusted its monetary units to conform to the higher level of prices there is no pressure on prices on this account. Furthermore, a large amount of gold formerly in hand-to-hand circulation passed out of circulation and has been added to the central bank reserves. The gold reserves of 36 countries increased approximately 100 per cent from the outbreak of the war to June 30,1930. The increase is much larger than the average increase of prices in any of the important countries, at any time since 192.5. As gold in the central banks of issue is far more effective for all business purposes than gold in circulation, the gold scarcity argument has little basis as applied to this time. The abnormal distribution due to the war was to the disadvantage of business everywhere. Credit was scarcer and dearer in some countries. The inflation in this country might have been greater had the production of gold been greater. The argument supporting the theory of a scarcity of gold assumes as fundamental that general price changes must be accounted for by changes in the price equation on the side of money. This is disproved in every period of business depression. A downward price movement is characteristic of every period of business recession. Important discoveries of gold must be made even to maintain present gold production, in the face of which the world's business is bound to continue increasing. It cannot be doubted that some way will be found

Jan 1, 1931

By John Gross

The study of the energy used in crushing operations has advanced from a period of perplexing confusion to one of greater clarity. Only within the last few years has any true conception of the work in crushing been possible, owing to the chaotic state of theoretical knowledge. For some 20 years a controversy existed between those advocating the Rittinger law and those advocating the Kick law. The Kick law now appears to be definitely out of the picture, and crushing efficiency may be based confidently on the Rittinger theory. There also seems to be a generally crystallized conception as to the meaning and nature of sub-sieve material. There is needed a simple, direct method for determining surface on a crushed ore product, and also a simple and accepted method for size determination on minus 400-mesh material. The Crushing Law The Rittinger(l)‡ theory of crushing was advanced in 1867 and the Kick(3) theory in 1885. While the Rittinger theory might have been accepted without much question and actually had been accepted by many investigators, a serious doubt as to its validity was raised by Stadler(10) who upon purely theoretical grounds proclaimed the Kick "law" as the true law of crushing. According to Rittinger the energy required in successive steps in reduction increases geometrically, while according to Kick the energy increases arithmetically. These "laws" therefore are at variance, and the establishment of the true law was recognized as of first importance. Many simple experiments have been made to demonstrate the application of the Rittinger theory to crushing, and it would seem that its simplicity should favor its acceptance. Experimental evidence, however, was not convincing, as no reliable data could be obtained on the finer material from a crushing or grinding operation. Gates,(13) Bell,(19)

Jan 1, 1935

By J. A. Berger, R. J. Towner

The pjPocesses of polygonization and subgrain growth were followed in slightly stretched 99.99 pct A1 single crystals heated for cumulative times at 400°, 500°, and 600°C. Changes in sub-grain size and boundary angle were determined from measurements on X-ray micrographs. CAHN1, 2 studied polygonization in stretched and heated aluminum single crystals of 99.99 pct A1 using various techniques, including etch pits, Laue patterns, and a slight restretching of heated specimens to reveal small changes in lattice orientation by the direction of new slip lines. He found that kink bands, which had well-defined boundaries lying in a plane perpendicular to the slip direction (at least in the early stages of deformation), formed during stretching. Also, he noted that bending occurred about the <211> axis lying in the (111) slip plane perpendicular to the <110> slip direction. His studies of polygonization were largely confined to the kink bands rather than to the weakly bent matrix regions between bands. The minimum temperature required to bring about polygonization was established at about 450 "C. Guinier and Tenevin used a focusing Laue X-ray diffraction technique to study polygonization in aluminum single-crystal specimens of 99.99 pct purity. Stretching the crystals 5 pct in tension caused a widening of the focused Laue spots. After heating for 4 hr at 450°C, their method revealed no change in the specimen. Above 450°C polygonization was detected and further annealing near 600°C led to subgrain growth. They concluded that the orientation of the crystal relative to the axis of deformation had no marked effect on polygonization. Gay and Honey-combe4 using an X-ray microbeam technique found that polygonization did not occur in a stretched aluminum crystal heated at 250oC, although some decrease in the yield strength occurred. When the temperature was raised to 475oC, the asterism became broken up as a result of polygonization. Honeycombe5 noted that reflections on X-ray mi-

Jan 1, 1961

The movement for Federal endowment of engineering and industrial research was revived early in the present Congress by the introduction of two bills into the Senate. The first bill, introduced by Senator Smith of Georgia, provides for the establishment of an engineering experiment station in each state under the direction of and in connection with some university, engineering school, or land-grant college. The state legislature of each state is authorized to designate the institution best equipped to conduct the work but wherever the land-grant college has facilities approximately equal to those of the other institutions of the state, it shall be designated. All designations of institutions are made subject to the approval of the Secretary of Commerce. The Secretary of Commerce is authorized to secure practical uniformity of methods, and efficiency and economical expenditure of funds by indicating such lines of work as shall seem to him important from a military; naval, industrial or national standpoint, but the responsibility for the initiation and conduct of research shall rest with the individual engineering experiment stations. Uniform standards of research are further provided for by making each experiment station a depository of the Department of Commerce and the Bureau of Standards, and the work of each station shall conform to the standards established by the U. S. Government through said bureau, which may whenever practicable utilize the facilities of the station for the prosecution of research.

Jan 8, 1919

By C. F. Cornell, R. C. Emmett, D. A. Dahlstrom

FOR many years the disk-type and cloth-covered drum filters have found widest application in liquid-solids separation, which uses continuous filters. The disk type is less expensive, occupies less floor space per square foot of filtration area, and requires negligible down time for filter media changing. However, because filter cloth is billowed out by the blowback in the cake discharge, it is very short-lived if the scraper blades are set too close. Consequently cake weight is very important in assisting cake discharge, which normally necessitates a minimum cake thickness of 3/8 to ½ in. Also, the vertical position of the disks eliminates the possibility of efficient cake washing for removal of soluble values. The disk-type filter is generally limited, therefore, to applications that require no cake washing and form relatively thick cakes within the normal range of filter cycle times. The conventional cloth-covered drum filter is a more flexible unit, permitting wider variation in the percentage of cycle time devoted to cake formation, dewatering, or washing, as required by the application. Thinner filter cakes can be discharged because a horizontal line across the filter medium at the location of the scraper blade is equidistant from the edge of the blade at all points. The scraper blade therefore may be set a short distance from the filter medium or, where wire winding is not used, a floating scraper can be utilized so that the contour of the cloth can be followed. The drum filter is generally employed when there are difficult filtering slurries with resultant thin cakes or when cake washing to recover soluble values must be practiced. Difficulties sometimes encountered in continuous filter operation can be summarized in the following four categories: 1) Low filtration and/or washing rates due to blinding of the filter medium. 2) Poor cake discharge resulting from sticky cakes, filter medium blinding, or too thin a cake for the particular type of filter. 3) High filter media costs caused by short life and frequent down times for cloth changing. This results from blinding or from abrasion by the scraper blade when cakes are thin. 4) Blowback of filtrate at cake discharge because not enough air passes through the cake to purge the drainage area and filtrate lines during dewatering. To reduce or eliminate blinding tendencies several modifications have been tried, for example, cover-cleaning showers, blowback under the feed slurry, and snap-blow cake discharge. In many cases, however, this simply retards the rate of blinding, since the filter medium is kept clean at its outer surface only by these methods. As blinding usually occurs within or on the back of the medium, the operator is finally forced either to remove the cloth and scrub the medium intensively with a cleaning solution or acid-rinse it on the filter—all resulting in down time, short cloth life, and additional costs.

Jan 1, 1959

By Edwin Chance

DURING the last decade many conditions have been encountered that have materially increased the cost of the production of coal. As in most cases it has not been practicable to increase the selling price of such coal sufficiently to insure the necessary margin of profit, the mine management has been forced to avail itself of what might be termed unusual means that costs might be held at as low a figure as possible. The so-called efficiency engineer has been called upon, costly power plants have been built and machinery has been installed to replace manual labor wherever possible. Another aid used recently to secure economies through the more intelligent production of coal, is the chemist. As the coal industry, barring the production of byproduct coke, does not at once give evidence of its need of the services of the chemist, the writer will endeavor to point out a few of the services that this branch of the staff has been able to render. The preparation of coal in the past has been carried on entirely upon an empirical basis, that is, the criterion adopted has been an ocular inspection. Unfortunately, the appearance of a coal and especially of an anthracite, has but little relation to its fuel value, and as long as coal is purchased for the heat that &apos;can be obtained from it by its combustion, the quantity of such heat that is purchased must be one of the principal desiderata in selecting or preparing a coal. Were coals purchased for use as bric-a-brac or for exhibition in museums it might be both wise and just to purchase them upon their appearance. After 4 or 5 years of investigation the fact has been established that coals of very inferior appearance, and I now have special reference to anthracite, might and often did possess heating and burning properties superior to those possessed by, bright coals which in the past had commanded considerable and uniform premiums in the market. This being the case the question arose as to whether the trade could be convinced of this fact. While at first some difficulty was experienced in establishing the quality of such dull coals, still it was found that the real obstacle to the sale of these

Jan 4, 1916

By A. H. Tousley

The cement industry is on the horns of an economic dilemma. Within the last ten years, its over- capacity in the United States has varied from 139- 127% of demand (Fig. 1). The most direct effect of this is seen in cement prices, which reached a peak in 1960, retreated steadily through 1966 and only recently climbed back to the 1960 level again. With prices in a slump and production costs estimated to be up almost 30%, there has been a steady drain on cement profits. Since 1960, labor costs have increased 86% while fuel costs have risen 18%. Meanwhile, customer service costs have also soared owing to the competition for cement customers and the wider variety of available cement products. This search for sales advantage has in turn led to a higher Blaine number, which means more grinding and hence bigger mills, more power, and, once again, higher costs. New plants as well as expansions and revisions to existing plants are also costing more owing to higher

Jan 1, 1971

By THOMAS LEONBRD WATSON

I. INTRODUCTION. THE results embodied in this paper are based on a careful field- and laboratory-study of the lead- and zinc-deposits of the Virginia-Tennessee district, begun in the latter part of the summer of 1904 and completed in the spring of 1905, preparatory to the publishing of a State report .on them. A separate description of the individual deposits in Virginia is purposely omitted, since I have already described them in considerable detail in a State report. The Tennessee deposits are described here in some detail for the reason that no detailed record of them has yet been published. Practically, this paper summarizes the results obtained from a study of the geology of the ore-deposits of the district as, a whole. (I had the pleasure of visiting the deposits of Virginia and Tennessee with Dr. H. Foster Bain of the U. S. Geological Survey, in April, 1905. Figs. 21 and 22 are from photographs taken by Dr., Bail.) II. HISTORICAL. . The first authentic records of lead-mining .in Virginia date hack more than 150 years; and the old lead-mines at Austinville, on New river in Wythe county, V a., were the first to be worked. Colonel Chiswell, a native of Wales, and one of the earlier adventurers in southwestern Virginia, was one of the first operators of the Austinville mines. Chiswell&apos;s operations at Austinville commenced in the year 1750, and closed shortly after the beginning of the Revolutionary War, in the&apos; year 1776, covering a period of about 25 years. From that time to the present, mining has been carried on almost continuously in the Virginia area. For many years after the Virginia mines were operated, mining was confined exclusively to the lead-ores. The zinc-ores

Mar 1, 1906

By E. T. Dumble

(San Francisco Meeting, September, 1915) THE history of the several petroleum deposits of Texas and Mexico, or of the sediments in which they now occur, if the deposits are not indigenous to such sediments, is known in a general way only, but it nevertheless casts strong light on the conditions surrounding them and is of great importance in the search for and exploitation of then. The petroleum deposits of Texas are separable into two main divisions: 1. The deposits of northwestern Texas, which are directly connected with the Oklahoma fields to the north, and have no representatives at all in the Mexican area. 2. The deposits of the coastal area, which extend into Louisiana on the east and connect with those of the Mexican coast to the south. Early in the Pennsylvanian period a series of bituminous shales and limestones were laid crown over a broad area in Texas, Arkansas, and Oklahoma. These are known as the Bend series in Texas, the Caney shales in Oklahoma, and the Fayetteville beds in Arkansas. Following their deposition an uplift occurred, forming the Lampasas geanticlinal, which runs northeastward from the old Paleozoic land area of the Llano region toward Red River. The Bend series is petroliferous in places and has furnished a few producing wells on each side of the Lampasas uplift. This uplift forms the barrier and. dividing line between the two divisions of the Texas petroleum deposits. To the west of it, in waters which were the southern extension of the interior continental seas, in connection with the sediments and coal beds of the Pennsylvanian and Permian, great quantities of petroleum were deposited either as oil or as "potential petroleum." These sediments have been subject to very slight disturbance, and only very gentle folds. are found, with no signs of volcanic action in any part of the area. The conditions, therefore, indicate that the greater part, if not all, of the oil in this area is indigenous to the beds in which it is found.

Jan 8, 1915

By AIME AIME

The following changes of address of members have been received at the Secretary&apos;s office during the period of March 15 to May 1, 1907. This list, together with the list of changes of address published in Bi-Monthly Bulletin, No. 14, March, 1907, supplements the annual list of members corrected to Jan. 1, 1907, and brings it up to the date of May 1, 1907. The names of members who have accepted election during March and April, 1907 (new members), are printed in italics. The large number of changes of address since Jan. 1, 1907; shows the importance of publishing these changes as frequently as possible, and the Bi-Monthly Bulletin has. been selected as the means to present this information to the members of the Institute. By the simple method of cutting out these names and addresses and pasting them directly over the corresponding names in the annual list of members, the record can be kept practically up to date, and the value of the list correspondingly increased. For this purpose the changes of address have been printed only on one side of the page. The names of new members, being in italics, are readily distinguished from the others, and can be pasted in approximate alphabetical order on the margins of the pages.

May 1, 1907

By M. C. Manderson

The sharp drop in world phosphate demand that took place in 1975 due to temporarily high prices, now seems to be reversing itself. And prices for both phosphate rock and phosphate fertilizers, which declined dramatically from their 1975 highs, now appear to be bottoming out. This recent price weakness has delayed new mining ventures that had been planned for completion by around 1980. While there is ample capacity to supply near-term rock needs, the stage seems to be emerging for a better supply-demand and price environment in the late 1970&apos;s and early 1980&apos;s.

Jan 1, 1979

By E. A. Stevens

IT has been ascertained in recent years that certain rocktypes, geological formations and structural conditions may be used as fairly reliable guides, when prospecting in recognized mineral belts or mining districts, with a reasonable certainty of discovering "pay-ore;" and that such is considered as a practically established conclusion may be inferred from a perusal of the recent reports of the U. S. Geological Survey and the literature of the several scientific societies discussing minim, geology, and kindred subjects. Cripple Creek is no exception to this conclusion, and the rock-type or association, rather than the structural condition, is the most infallible guide.† These guides consist of four, possibly five, dike-rocks, three of which are extremely basic, while the fourth is an acid rock of an entirely dissimilar character. The basic rocks are nepheline-basalt, limburgite, feldspar-basalt and tephrite. There are grounds, however, for believing that the two latter are subdivisions of one type, and therefore will be described under one head. The acid rock is quartz-porphyry. Nepheline-basalt is-a rock encountered in but few localities elsewhere on this continent, and occurs in narrow dikes cutting various formations. When typical‡ it is composed of

Jan 1, 1913