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By Daryl R. Tweeton

The Bureau of Mines is investigating possible applications of geophysics to monitor leachate during in situ mining. Tomographic reconstruc-tion of seismic or electromagnetic crosshole data appears applicable. The tomographic program BOMTOM (Bureau of Mines tomography) was written and then used to investigate reconstructions with synthetic travel time data. The calculations confirmed that without constraints, crosshole data do not provide unique solutions. The solution is not determined solely by the data, but is also influenced by the velocity guesses starting the iterative solution procedure. The effectiveness of constraints in combatting nonuniqueness was examined. The requirement that the velocity not vary laterally at the top and bottom of the pixel grid was effective. This constraint is realistic when the top and bottom of the grid represent dry and saturated re-gions, respectively. Limiting the maximum velocity improved reconstructions, but may not be applicable in practice. BOMTOM uses the simultaneous iterative reconstruction technique (SIRT) with straight ray paths. The program is efficient in use of memory, and can be run on a personal computer. A source code in FORTRAN is listed. A source code in BASICA and compiled executable codes in both languages are available from the Bureau's Twin Cities (MN) Research Center.

Jan 1, 1985

By Kenneth Eilerts

[Efficient and econonic production of ?etroleum requiros knowledge of the propertios of rescrvoir fluids a:$. their characterintics of flow throayh porous forclntions. The cllanga in propertie s and flow characteri s- tics of fluids when their corosition is altercd cs a rnsult of reservoir- pressure decliae is of 'mecial i~ortenct? ir, planning wall-spaAng pro.yama and production schedules. Rct~ntion of the ~eatent poscible quantity of dissolved gac in the rescrvoir liquid gnneml'y is recognized cs ess~ntisl to mxim ultimzte recoverj of oil fro3 the underground reecrvoir. Ilo:rever, pro6uction mothodn tending to mintain gis in solution in the oil and re- sulting in the optimm ocolo~ic recgvery of oil not only vary from field to fiold but also my have to be changed from time to time in a given field as it is being depleted of its recoveraklo oil. Const vestly there is need tc investigztc tY.e propertiec of resa:-voir f kids corresponding to successivc stages of reservoir depleJ&ion with the view of obtnining infomation oacential to efficient prcriuctian practices.]

Jan 1, 1939

By Robert J. Evans

The monorail bridge conveyor (MBC) is a prototype continuous face haulage system that was surface tested and evaluated by the Bureau of Mines. The MBC consists of a series of cascading belt bridge conveyors suspended from roof-supported monorail track. Tests were conducted to determine MBC haulage capability, maneuverability, power consumption, and reliability using rigid and chain-suspended monorail track installations. Subsequent modifications to improve operation and reliability made during surface testing are described. Mining plans were devised to show potential MBC installations for room-and-pillar, longwall development, and shortwall mining sections. Compatibility tests were conducted with the Bureau's prototype hopper-feeder, to provide additional surge capacity and lump-breaking capability. Results from the surface test program, along with modifications to improve system operation and reliability, indicate that the MBC has the potential to perform success- fully in an in-mine trial.

Jan 1, 1987

By R. F. Stewart

A key step in changing coals to fluid fuels and chemicals is the conversion of coal to synthesis gas by gasification with steam and oxygen. As oxygen represents one of the largest single expenses in gasification, its cost is a vital factor in the economy of the process. At present, the most economical method for producing tonnage oxygen is by the conventional rectification of liquefied air. Several alternate methods have been proposed for producing oxygen from air: (1) methods based on physical or chemical sorption of oxygen from air by liquids or solids or (2) the oxidation of certain inorganic com-pounds to higher oxides unstable at higher temperature levels. Economic limitations are discussed by which these methods may be evaluated. Chelated metals of the salcomine type are promising chemical sorbents of oxygen from air. This report covers a study of the reversible sorption of oxygen by salcomine and other chelates. The presence of water in the salcomine structure was verified; it is the loss of this water that causes slow deterioration of salcomine during cycling.

Jan 1, 1959

By Robert H. Merrill, James V. Williamson, David M. Ropchan, George H. Kruse

In- situ rock stresses were determined by flatjack and borehole - deformation methods . Estimates of the stress distribution around a flatjack were obtained by a combination of flatjack and borehole - gage techniques . The investigations were part of a study , conducted jointly by the State of California and the Federal Bureau of Mines , to determine the stress in rock at the site of an underground powerplant for the Oroville Dam near Oroville , California . The stress distribution around each of three flatjacks was nonsymmetric ; however , stresses obtained from 9 flatjack and 157 borehole measurements are considered reasonably accurate for engineering purposes . The stress near the edge of the openings is between 800 and 1,600 psi ; the stress in the undisturbed rock is approximately 500 psi , nearly hydrostatic .

Jan 1, 1964

By A. G. Loomis

METHODS for measuring relative permeability as a valid function of saturation were compared by the. Bureau of Mines, using core samples from representative oil-productive California formations, from the Bartlesville sand in Oklahoma, and from synthetic samples. Measurements for gas-oil systems were made by steady-state dynamic, unsteady-state displacement and two stationary-phase methods. Measurements for water-oil systems were made by the unsteady-state displacement method. As the ratio rather than individual relative permeabilities is measured by the last method, three methods for calculating individual relative permeabilites from their measured ratio were compared for gas-oil systems and two methods for water-oil systems. Errors arising from capillary discontinuities, such as the end effect and stabilized-zone flow, are discussed and evaluated; possible errors rocs arising from turbulant flow are also examined. The inapplicability of non-steady-state methods for water-oil systems that are not definitely oil-wet is discussed in detail. Measurements of relative permeability to both gas and oil can be made quickly and accurately by the steady-state dynamic method when rates of flow of the two phases are sufficient to minimize the capillary discontinuity at the outflow end of the sample. At such rates relative permeability-saturation measurements are essentially independent of the rate of flow. The steady-state method wits modified by a dispersion section at the inflow end of the sample acid designated tie dispersed-feed method.

Jan 1, 1962

By Kenneth M. Maas

The Bureau of Mines inventoried the land in southwestern Alaska to classify ownership and availability and compared this land with known mineral terranes and mineral deposits. This report discusses and quantifies the potential for favorable location of mining claims for metalliferous (locatable) mineral deposits. Of the nearly 24 million acres that constitute the study area, approximately 3.6 million acres or 17% are available for mineral location, 3.4 million acres or 14% are available with restrictions, and 17 million acres or 71% are unavailable. Mineral terranes are known to underlie about 7.8 million acres or 33% of the study area; 3 million acres or 38% occur on land available for mineral location, 1.3 million acres or 17% occur on land available with restrictions, and 3.5 million acres or 45% occur on unavailable land. The State of Alaska has opened over 91 % of its land in the study area to mineral location; in comparison, the Federal Government allows mineral location on 0.07% of the land under its jurisdiction. There are 117 known mineral deposits or occurrences within the study area, including 77 lode deposits and 40 placer deposits. Of the 41 lode deposits occurring within a mineral terrane, 2 occur on available land.

Jan 1, 1988

By Chas. F. Jackson

This circular is an abstract of a manuscript-completed in August 1932, which cannot be published in its entirety due to lack of printing funds. It was originally planned to publish the manuscript as one of a series of bulletins dealing with the mining and milling of ores of the principal metals. Because of the common association of lead and zinc minerals in many ore deposits, and because a considerable proportion of the zinc produced in this country is obtained as a by-product of lead mining or vice versa, it seemed necessary to treat the mining and milling of lead and zinc ores in the same volume.

Jan 1, 1934

By Oliver Bowles

"The town of Monson in Piscutaquis County, Maine is the, center of an important site industry. Monson slate has a nation-wide reputation, particularly for electrical switch boards, and the deposits have been worked for the manufacture of such products for many years. Open-pit quarrying is the method most commonly employed in obtaining slate. Underground methods have been used in the Peaon Bottom district near Delta, Pennsylvania, but the quarries that were thus operated are now abandoned. Underground methods have been used more extensively in foreign countries, the most famous example being the slate mines at Angers in France, where an over-head stoping method has been employed successfully for many it is only under special conditions that underground methods can be successfully used. If the deposit is wide and relatively thin, or if the material is too unsound to constitute a safe roof, open-pit methods must be used, for slate is too low-priced a commodity to justify the heavy expense of any timbering methods. It is only where the deposit is relatively narrow, of great depth, and sufficiently sound to afford a strong roof that ordinary mining may be employed.The best slate beds in two of the three quarries operated at Monson are no worked by underground methods. The chief bed worked by the Portland Monson Slate Co. is 10 feet thick, stands vertical and strikes N. 63º F. The slaty cleavage is vertical and crosses the strike of the beds at an angle of 5 to 10°. The grain or second direction of splitting is vertical and perpendicular to the cleavage. In addition to the 10-foot bed, to 2-foot beds and one 5-foot bed are available but are not now utilized. In the Monson Maine Slate Co. quarry (the old Pond quarry),a greater number of beds available, but at present quarrying is confined to a single bed about 9 feet thick which dips 30º S.E. and strikes N. 47ºF. The slaty cleavage is vertical and strides N. 45º F., while the grain strikes N. 45-50º W. and is also vertical."

Nov 1, 1920

By Frederick L. Hoffman

These extracts are sufficient for the purpose of emphasizing the practical difficulties of averaging iron-mining conditions so as to make general vital statistics concerning iron miners useful Tor scientific. purposes. It is self-evident that conclusions based upon iron miners, so called, working largely above ground and employed chiefly in open-cut blasting ~perations or the management of steam shovels, etc., can not be made to apply to miners working continuously underground with an exposure of dust and other conditions quite similar to underground mining methods in the extraction of gold, silver, copper, lead, and other ores. The so-called "milling" process as practiced on the Mesabi Range may here be referred to, the same being explained in the report of the Immigration Commission to consist "in the sinking of a shaft on the edge of the ore body from which a tunnel is run in under the ore and connected with a vertical, funnel-shaped hole from under the surface, through which the ore is 'milled' down into the tramcars placed under the opening under the tunnel. After being loaded at the bottom of the funnelshaped hole, the cars are run out to the bottom 0.£ the shaft. where the ore is dumped into skids or elevators and raised to the ~urface and unloaded into the tipple, where it is loaded into thecal'S ready for shipment." It is properly pointed out that the so-called " milling" process employs some of the features of both the open-pit and underground methods of mining. For these and many other reasons it is self-evident that general statistics concerning iron mining are quite likely to be inconclusive and possibly seriously misleading. Aside from the foregoing the problem is seriously complicated by the extensive employment of foreign labor in the iron-mining ind ustries of the Lake Superior districts and of Negro labor in iron mining in Alabama. Within recent years, according to the report of the Immigration Commission, a considerable displacement has occurred in t~e quality of labor employed in iron mining, the displacement bemg referred to as "progressive," in that one race or group of races has entered the region and taken up the work offered in the lower occupations, the race or races already holdinz such positions having. moved up in the scale of occupation leaving the field to the newcomers. This statement is quite suggestive in that it indicates a comparatively short average trade life or trade exposure, quite at variance with the relatively long average ascer- MINES, QUARRIES, ORE REDUCTION, AND SMELTING. 377 tained for the iron mines of New <Tersey. It is said in the report of the Immigration Commission that- The Scandinavians and the other northern European races have given way to the Finns and Slovenians, and in the open-pit mines the Finns and Slovenians have given way to the south Italian, Montenegrins, Croatins, and other southern European races. In the underground mines the common labor and mining is chiefly done bv Finns and Slovenians because the races from the southern countries can not stand the heavy physical work required in this kind of mining. Here, too, is found the same upward movement, for formerly the English (Cornishmen) and Scandinavians' were in the lower occupations in the underground properties, At present the south Italians, Serbians, Montenegrins, and Croatians are performing the most menial work and are the races who are now at the foot of the scale of occupations. It is a matter of conjecture on the ranges as to who will push these races up or whether they will remain the commou laborers of the region. Inquiry was made into the prevalence of diseases OIl the ranges, but more with reference to outside sanitary conditions than to occupational exposure. The most common diseases on the ranges, however, were ascertained to be pulmonary tuberculosis and typhoid fever, and to a lesser extent smallpox and venereal diseases. With -cgard to pulmonary tuberculosis it is said that the disease is most Eevalent among the Finns and the Swedes, and is chiefly imported, I'here is no reference to a possible connection between disease occur- ~ence and occupational conditions, above or below ground, but there .s no evidence that this aspect of the iron-mining industry was made .he subject of a special investigation.

Jan 1, 1918

By Sidney Katell, JOHN H. FABER, BRYCE L. MADDOX

The information abstracted from the various publications appeared in the magazines under such headings as Business and Industry , Chemical Engineering Developments , Companies in the News , Headlines of the Month , Industrial News , Industry , Refining and Gas - Processing News , Refining News , What's Happening , and others . Although most items are related to chemical and petroleum plants , a few pertain to related fields , such as markets , drilling costs for petroleum , and field prices of crude oil . Certain articles discuss various aspects of cost -estimating procedures or description of processes . Cost bibliographies prepared by other groups are discussed in items 70 and 271. The two references can be considered as supplemental to this report , since the amount of overlap in the contents is insignificant .

Jun 15, 1957

By Daniel Harrington

On the night of June 8, 1917, the flame of a carbide lamp accidentally set fire to the uncovered and frayed insulation of an armored power cable near the 2,400-foot level of the North Butte Mining CO.'s Granite Mountain shaft. How this, insulation accidentally became exposed is explained on page 15. The highly flammable oiled fabric set fire to the shaft timbers, and as this is a downcast shaft the fire spread with great rapidity, soon filling the mine workings with smoke and gas. At the time 410 men were working underground, 247 of whom escaped by various means, but most of the 163 remaining were probably overcome soon after the fire started, and perished. Only two men were actually burned. The cause of the disaster was purely accidental. The immediate effect was the unexpected reversal of normal conditions; the ultimate effect was great loss of life and the destruction of the main hoisting shaft, putting it temporarily out of service. The work of rescue and fire fighting continued eight days. The following pages present an attempt to draw some practical conclusions and suggestions from this disaster. The property of the North Butte Mining Co. consists of about 220 acres in the northeastern part of the Butte district, Montana. Next to the Anaconda Copper Mining Co. it is the largest producer of the district. In 1916, the year before the disaster, there were 1,160 men employed. The output was 560,947 tons of ore, which yielded 24,498,181 pounds of copper, 1,047,063 ounces of silver, 1,712 ounces of gold, and 412,953 pounds of zinc. The profit was $2,479,595. The total development work for that year was 21,694 feet. During the first half of 1917, the year of the accident, the daily tonnage of ore averaged 2,000, an increase of 400 tons over that of the year 1916.

Jan 1, 1922

By Lloyd Williams, H. K. Gibbs, William L. Crentz, J. W. Miller

"Reserves This investigation shows that the Poplar Creek is the most important bed in Scott County from a production standpoint. Although the Poplar Creek bed contains the largest reserve, the Big Mary has a larger recoverable reserve. Estimates of reserves also have been made for the Pewee, Red Ash, Windrock, Upper Pioneer, Jellico, and White Oak beds.Known measured and indicated reserves of coal, based on a minimum bed thickness of 14 inches and on 1,800 short tons per acre-foot of coal in place, are estimated to be 143 million tons as of January 1, 1954. Of this total, 74 million tons is in beds 28 inches and more thick. Areas in each bed were omitted from the estimate because available data relative to the bed characteristics are too meager for making an estimate that conforms with the definitions of measured and indicated coal adopted for this study. Should future drilling or development prove reserves in these areas, such reserves should be added to the total estimated reserves.Recoverable reserves of coal are estimated in beds 28 inches and more thick. This thickness is about the minimum now being mined by hand loading onto conveyors in the Appalachian region. The weighted average recovery for all beds in Scott County, as determined by this investigation, is 52.4 percent. This percentage is based on the total thickness of coal in the bed (less partings three-eighths inch or more thick) rather than on the thickness of the coal mined. Based on the weighted average percentage of recovery for all beds in Scott County, the recoverable reserves of coal are estimated to be 39 million tons as of January 1, 1954.Coal Analyses Chemical analyses of coal samples taken for this study show that the coal in Scott County is of high-volatile a bituminous rank except the Upper Pioneer bed, which is shown to be high-volatile B bituminous. The Pewee bed shows typical low-sulfur characteristics. The high ash and sulfur in the Big Mary are characteristic of that bed. The Poplar Creek is moderately low in ash and sulfur in areas where there is no parting in the bed."

Jun 1, 1956

By Gustav Wade

"INTRODUCTION Analyses of samples of crude oil from several Texas oil fields have been published from time to time in Bureau of Mines reports, some of which are out of print, but many other analyses of Texas crude oils have not been published. The purpose of this paper is to make available in condensed tabular form under one cover all analyses of the Texas crude oils that have been examined by the Bureau of Mines.DIVISION OF TABLEThe table of analyses is divided into six parts in accordance with the geographic subdivisions of the State. (See fig. 1.) This grouping of the oils corresponds only in a general way with the principal formations in each area from which oil is being produced. In general, the principal oil-producing formations in the Texas Panhandle and West Texas areas are of Permian age; those of North Texas are of Pennsylvanian and older ages; those of the East Texas Basin and of Central Texas are of Cretaceous age; and those of the Texas Gulf Coast are of Eocene and younger ages.For convenience in presentation the name of the geologic age has been assigned to each group of the table although same of the oils included in the group may be of another age.Group 1 includes oils of Permian age produced in the Texas Panhandle area, which comprises the following counties: Dallam, Sherman, Hansford, Ochiltree, Lipscomb, Hartley, Moore, Hutchinson, Roberts, Hemphill, Oldham, Potter, Carson, Gray, Wheeler, Deaf Smith, Randall, Armstrong, Donley, Collingsworth, Parmer, Castro, Swisher, Briscoe, Ball, and Childress."

Dec 1, 1934

By P. -É. Boileau, M. Smets, T. Eger, J. Boutin

Long-haul dump (LHD) vehicles used in underground mining are known to expose workers to important levels of whole-body vibration1. These vehicles are generally designed without suspension and may be categorized as small or large LHDs depending on whether their respective load capacities are lower or larger than 3.5 cubic yards. While the majority of older vehicles are equipped with a rigid or unsuspended seat, more recent LHDs often incorporate a suspension seat. The objective of this study was to define the vibration spectral characteristics of most commonly encountered large and small LHD vehicles operating in mining operations. This was done in an effort to categorize the vehicles in terms of vibration spectral classes to be reproduced on a laboratory whole-body vibration simulator to assess the vibration attenuation performance of a typical LHD suspension seat. Methods Vertical vibration measured at the seat attachment point of 8 small and 8 large LHD vehicles operating underground in typical mining operations under loaded and unloaded conditions was considered as the basis for defining the spectral classes. By regrouping the data collected for each LHD vehicle size and load condition, the overall distribution of acceleration power spectral density (PSD) of measured floor vibration was determined over the 0.5 to 20 Hz frequency range. Mean and envelopes of maximum and minimum values of PSD spectra were computed to define the spectral classes, along with the corresponding values of frequency weighted rms acceleration determined in accordance to the ISO 2631-1 standard2. These spectra were further used to calculate the displacements needed to drive a whole-body vibration simulator consisting of a platform supported by two servo-hydraulic actuators having a total stroke of ±100 mm. For validation purposes, the vibration acceleration spectra measured on the simulator were compared with the target spectra representing the spectral classes. Finally, the vibration transmissibility characteristics of a typical suspension seat were determined under sine sweep excitation using both a rigid mass load and a human subject having a mass of 62 kg and 85 kg, respectively. The SEAT value, representing the ratio of seat to base frequency-weighted rms acceleration, was further measured under each of the defined LHD vibration spectral classes by loading the seat with an 85 kg subject. Tests were repeated three times and the mean SEAT values were determined to assess the seat’s ability to reduce exposure to whole-body vibration in LHD vehicles. Results Three spectral classes applicable to both loaded and unloaded conditions were defined as shown in Figure 1: one for large and two for small LHDs. The influence of load on frequency-weighted rms acceleration was found to be negligible for large and Class I small LHDs, while a shift of the peak acceleration PSD to lower frequencies was noted for the loaded vehicles. The influence of load was found to be more important for Class II small LHDs. Table 1 provides a

Jan 6, 2006

This report summarizes the cost of U.S, mining and milling industry compliance with the Environmental Protection Agency (EPA) interim water quality guidelines for waste discharges. Applicable excerpts from Public Law 92-500 are stated and interpreted in conjunction with the guidelines being used for implementation of the law. Over 200 U.S. Army Corps of Engineers applications for discharge permits were used to develop the quality and quantity data base needed to estimate the cost to comply with EPA guidelines, Cost of three basic treatment methods were considered: Aeration, addition of lime, and sedimentation. From the process design, cost-capacity graphs were developed to consider maximum flow rate, maxi lime addition, and average flow rates. The graphical method used in this evaluation should provide a reasonable guide to the effect of waste treatment and, therefore, Public Law 92-500 and corresponding EPA guidelines on the mineral processing industry. The cost of complying with the EPA guidelines will have the effect of prompting the mining industry to minimize the production of waste water and of undertaking some additional treatment, Two case studies are presented to illustrate efforts that might be fruitful for minimizing waste water production and for treatment of combinations of acid mine drainage, mill wastes, and metallurgical process wastes when treatment is deemed necessary.

Jan 1, 1975

By Guenter F. Lehmann

This report summarizes the results of the development and testing of a prototype monorail suspended bridge conveyor (MBC) system as a method of continuous haulage In underground mining applications. Included are the results of full scale, surface and underground testing of the complete MBC system. Conclusions drawn from these results, together with recommended modifications, supports the viability of the MBC system.

Jan 1, 1988

By Thomas O. Glover

Cameroon continued to enjoy sustained economic growth that began with its independence in 1960. Growth in the gross domestic product (GDP) averaged 2.8% per year during the 1960&apos;s and the first half of the 1970&apos;s. Starting in 1976 and for the succeeding 10 years, the GDP accelerated rapidly owing to the coming on-stream of Cameroon&apos;s small but domestically significant offshore oil industry. In 1985, the GDP grew by 7.8%, but in 1986, it was only up 5.5%. The country&apos;s sustained economic growth in dollar terms of gross national product (GNP) per capita reached $1,075 in 1986. The ranking in GNP per capita by the International Monetary Fund put Cameroon in the middle-income category for developing countries. The sustained economic growth rate up to 1986 was due to the injection of income from oil into the economy, but crude oil price reductions in 1986 brought a slowdown. In 1986, crude oil production grew to 200,000 barrels per day, an increase of 8.2% from that of 1985. Most of the oil came from the Société Nationale Elf Aquitaine (SNEA) wells in the multifield Rio del Rey complex. Additional output came from the Moudi Field operated by Compagnie Française des Pétroles S.A. Proven oil reserves in Cameroon were 540 million barrels. At 1986 production rates, and in the absence of further discoveries, Cameroon will have exhausted its recoverable oil reserves by the year 1995. Owing to worldwide crude price reductions, the country&apos;s oil income fell 60% between 1985 and 1986, from $1.82 billion2 to $0.72 billion. Cameroon&apos;s refinery operator commenced operating the Sonara refinery in 1981 at Point Limboh. Sonara&apos;s capacity of 43,000 barrels per day was small by most standards. In 1986, natural gas reserves, estimated at 100 billion cubic meters, were not produced commercially because there were no domestic users. Proposals for a multibillion-dollar liquefied natural gas plant at Kribi had been submitted; however, work on the plant had not commenced.

Jan 1, 1988

By Jack O. Jones

The Furnish mine, Caharrus County, W. C., was operated intermittently until 1905 as a gold mine. Scheelite was discovered by A. L. Mash in the mine dumps of the Furniss and Phoenix mines, and he later informed the Bureau of Mines of his discovery. The Bureau of Mines, in two projects at the deposit in 1948 and in drilled 12 holes totaling 1,706.6 feet, examined and sampled the underground workings, excavated by bulldozer and hand, 3,155 linear feet of trenches and collected numerous samples for assay. The best scheelite shown; was found in the underground exposure of the Furniss mine.

Jan 1, 1950

By R. F. Zaffarano

Data presented on the physical characteristics of the reservoir oil, Aneth field, represent the initial phase of a study of Paradox basin reservoir oils being made by petroleum engineers of the Federal Bureau of Mines, Petroleum Research Center, Laramie, Wyo. The purpose of the study is to determine the original reservoir-oil characteristics in several important new discoveries in the Paradox Basin and to investigate correlations between the properties of these reservoir oils and structural or areal position within the basin, If migration is limited and oil accumulates near its source, then it seems probable that few differences should be found in the composition and characteristics of reservoir oils occurring in given age rocks and within the confines of a geological basin. Within these limits, conditions that effected the formation of oil and its transfer from parent to storage rocks probably were rather uniform in an area the size of most of our geological basins. However, if oils should migrate considerable distances, it seems logical to expect that the relative quantities of gas and liquid components may differ in traps occurring along the direction of migration, corresponding with the theory of differential entrapment (5).4/

Jan 1, 1959