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By Donald Jaffe, Michael B. Bever

The solidification of Al-Zn alloys (2 to 70 pct Zn was investigated at different rates of solidification. The resulting structures were studied; the amounts of nonequilibrium eutectic were measured and compared with the amounts calculated on the assumption of no diffusion in the solid. The compositions of the cored primary constituent were investigated by quantitative autoradiography after activation of the zinc by neutron irradiation. These compositions were also determined from microhardness values. IN a recent investigation of the soltdification of aluminum-rich AI-Cu alloys,' the amounts of non-equilibrium eutectic were measured and compared with the amounts calculated on the assumption of no diffusion in the solid. The compositions of the cored primary constituent were investigated by quantitative autoradiography. The work reported here extends the investigation of nonequilibrium solidification to the Al-Zn system in the range from 2 to 70 pct Zn. In addition to autoradiography, microhard-ness values were used to determine compositions on a micro scale. Solidification Experiments The alloys contained approximately 2. 6, 12, 20, 30, 50, and 70 wt pct Zn and the balance aluminum. According to published diagrams the eutectic reaction occurs at 382°C between the eutectic liquid (95 pct Zn), a (82.8 pet Zn), and $ 498.9 pct Zn). Solid-state reactions at lower temperatures (due to the miscibility gap between 350" and 275"C, the eutectoid at 275'C, and the precipitation from supcrsaturated a) did not affect this investigation. Even if they occurred to any appreciable extent, they did not alter the evidence pertaining to the solidification structures. The alloys had to be of high purity to avoid radioact~ve contamination during activation. The aluminum analyzed 0.015 pct Si, 0.009 pct Fe, less than 0.004 pct Cu, and less than 0.006 pct Mg with traces of sodium and titanium; the zinc was reported to be at least 99.99 pct pure with traces of iron and magnesium. The alloys were prepared under argon in an induction-heated, bottom-pouring furnace, and poured into a coated steel mold, which could be preheated to temperatures up to 700°C in order to control the rate of solidification. The pouring temperatures ranged from about 40" above the liquidus for 2 pct Zn alloys to about 130°C above the liquidus for 70 pct Zn alloys. As soon as the melt entered the mold, the readings of a thermocouple placed % in. above the bottom of the mold were recorded by a recording potentiometer. Cooling at the rate induced by the initial temperature of the mold was continued to a temperature 100°C below the liquidus; the mold with its contents was then quenched in icy brine. Quenching from a fixed interval below the liquidus was used to provide a standardized procedure, since the solidus and liquidus temperatures and the interval between them vary greatly over the composition range investigated. The temperatures from which the samples were quenched were below the equilibrium solidus, but under nonequilibrium conditions some liquid was still present. This residual liquid solidified during the quench. The samples measured 314 in. diam and 11, in. height. Drillings for chemical analysis were taken

Jan 1, 1957

By Alesse V, Belardi G

A new class of collectors, Mercapto-Benzo-Oxazoles (MBO), exerting selective action on copper sulphides in the presence of Pb, Zn and Fe sulphides (galena, sphalerite and pyrite), has been synthesised in co-operation with Enichem's Donegani Insitute. The collectors have a mixed aliphatic-aromatic structure and contain functional groups which form chelates with copper. Some reagents of this class having hydrocarbon chains of various lengths have been laboratory tested on a complex sulphide ore containing chalcopyrite, galena and sphalerite in pyritic gangue. Comparative flotation tests have permitted selection of the best collector for chalcopyrite, namely Methyl-Mercapto- Benzoxazole (MMBO). Systematic flotation tests have been performed with this reagent, varying collector concentration, grain size of the feed, pH and flotation time. The results obtained show that the synthesised collector is much better than potassium-amylxanthate (KAX) as regards selectivity towards Pb and Zn. Moreover, it is possible to work at natural pH (6-7) and the flotation rate is higher. In fact in the rougher stage with 80 g/t of collector at natural pH, a copper grade of 7.14 per cent was obtained with a recovery of 73.87 per cent, while the grade with KAX did not exceed 2.11 per cent for a recovery of 73.54 per cent. The amount of Pb and Zn reporting in the copper concentrate was eight per cent and ten per cent respectively, while with KAX it was no lower than 24.34 per cent and 22.71 per cent in that order. After two minutes flotation a copper grade of 5.2 per cent with 52 per cent recovery could be attained, against a grade of 2.5 per cent and a recovery of 44 per cent in the case of KAX. The efficiency of this new collector has been ascertained on two samples of complex sulphide ores of diverse mineralogical composition.

Jan 1, 1993

By H. F. Yancey

This report, dealing with the separation of coal from its associated impurities by means of a pulsater-type jig, continues the series of reports that have been issued by the Bureau of Mines, in which detailed study has been made of the efficiency and mechanism of separating coal and impurities in various coal-cleaning appliances. The previous reports have dealt with the piston jig, coal-washing table, pneumatic table, and Baum-type jig. Such studies of the separation accomplished by any form of concentration device are essential and necessarily preliminary to any intelligent attempt to improve the performance of such equipment Object and Plan The pulsator-type jig was developed recently by G. A. Vissac. Although two articles(2) describing plants using this typo of cleaning unit appeared in 1936, both dealt principally with plant design and layout rather than with plant performance The object of the stork described in this report was to determine the efficiency of the separation made by the pulsator jig on a sized feed, the specific gravity at which the separation between coal and impurity was effected, and the influence of the specific-gravity composition of the coal on the character of the separation made.

Jan 1, 1938

By H. F. Yancey

This report, dealing with the separation of coal from its associated impurities by means of a pulsator-type jig, continues the series of reports that have been issued by the Bureau of Mines, in which detailed study has been made of the efficiency and mechanism of separating coal and impurities in various coal-cleaning appliances. The previous reports have dealt with the piston jig, coal-washing table, pneumatic table, and Baum-type jig.5/ Such studies of the separation accomplished by any form of concentration device are essential and necessarily preliminary to any intelligent attempt to improve the performance of such equipment Object and Plan The pulsator-type jig was developed recently by G. A. Vissac. Although two articles(2) describing plants using this type of cleaning unit appeared in 1936, both dealt principally with plant design and layout rather than with plant performance The object of the stork described in this report was to determine the efficiency of the separation made by the pulsator jig on a sized feed, the specific gravity at which the separation between coal and impurity was effected, and the influence of the specific-gravity composition of the coal on the character of the separation made.

Jan 1, 1938

By Wharton P, Voigt R

In order to do the discharge estimation better, it is valuable to find out appropriate formulas for estimating discharge in various pits, based on accumulating data, summarizing discharge patterns applying optimum seeking method and principle, by seeking redical exponent with help of the method of exhaustion, as well as testing and making statistics, in accordance with the quality standards established by our practical experience.

Jan 1, 1988

By Paul J. Axtell

The results of in-situ geophysical cross-hole tests on improved soil by soil mixing (SM) and jet grouting (JG) are described. This testing was conducted on soil improved by SM and JG columns constructed in the downstream free-field of Tuttle Creek Dam near Manhattan, Kansas as part of the seismic retrofit. Results of similar geophysical testing performed on untreated soil in the vicinity of the Downstream Test Program (DTP) area, as well as beneath the embankment at several locations, are also described and used for comparison purposes. In-situ shear moduli are also compared with those determined in laboratory resonant column tests. The increase in stress wave velocities and associated shear moduli by SM and JG treatment are presented for use in liquefaction potential and seismic deformation analyses of SM or JG treated soil. This data is required to determine the decrease in liquefaction potential and earthquake-induced permanent deformations due to SM or JG with respect to that of untreated soil.

Jan 1, 2008

Dump Truck Kenworth Motor Truck Corp. is beginning full scale production of its new heavy-duty, end-dump earth mover, model 801, a truck engineered for earth moving under the most adverse operating conditions. Payload capacity of the Kenworth earthmover is 30,000 lb and it is over-tired for safety, flotation and high tire life. The truck's body capacity, struck measure, is 9.9 cu yd, with heaped [ ] load at 11.9 cu yd. The earth-mover has a full anti-friction bearing mounted, power assisted steering gear, simplified controls, minimum turning radius and wide axle track to insure ease of handling, maximum maneuverability and high stability. The offset cab of the Kenworth visibility for the driver, before and after. Circle No. 1 Safety Equipment A compact, safe, and efficient valve assembly approved by the United States Bureau of Mines for use with MSA air line respirators, abrasive masks, and abrasive helmets has been developed by Mine Safety Appliances Co. The new MSA continuous air flow control valve regulates air flow from a compressed air source to an operator using respiratory protective air line equipment. Three parts-a centridge container, a cartridge and the air flow check valve-comprise the entire assembly of the control valve. A position action adjustment knob on the cartridge container regulates the amount of air flowing to the operator. The valve can be detached from the air line instantly by pressing the trigger on the cartridge container near the check valve. As the trigger detaches the hose, the spring loaded ball-type valve, which is attached to the end of the hose, automatically stops the flow of air. Circle No. 2

Jan 1, 1952

By J. M. Barker

The concept of global-market access through transportation efficiency is a concept whose time has come. The basis of this approach is customer satisfaction—the higher the better. But beyond what seems almost too logical is the question of how to achieve this market access. All industrial mineral exporters face stiff competition. Factors include proximity of competitive industrial minerals and substitutes, pricing pressure, political and cultural differences, currency fluctuations, communication problems, trade finance restrictions, and transportation imbalances. The following discussion will focus on transportation activities in global competitiveness, but the producer with the larger offering of services will often make the sale, not necessarily the low-cost producer (Cook, 2002). Some key concepts for global-market access are “the market concept,” just-in-time delivery, quality retention, and global customer service.

Jan 1, 2003

By R L. Calhoun

A paper on High Pressure Air must start with the industry accepted definition of High Pressure Air and, for the reader who is unfamiliar with High Pressure Air systems, include basic information on which type of Drilling Rigs can benefit from the use of High Pressure Air. The operation of a modern Downhole Drill must also be reviewed.

Jan 1, 1976

By Michel Dupuy, Daniel Calais

The study of self-diffusion of plutonium in E phase has been carried out by the welded couples method. The tracer used was puZ4O which is detected by its X-ray emission (conversion lines of uranium which are computed between 13 and 21 kev). Intensities were measured with a scintillation counter. Each layer was removed in a direction parallel to the original interface with a grinding machine and a thickness measured with a pneumatic comparator. The concentration-penetration curves obtained were corrected for the effect of heating time from room temperature to annealing temperature and for the expansion due to phase transformations of plutonium. They were analyzed by the generalized Gruzin method. Self-diffusion of plutonium in E Phase is very fast cm per sec between 500" and 620°C) and the diffusion zones are 2 to 3 mm wide for annealing times ranging from 30 min up to 10 hr. The Arrhenius law gives the temperature dependence in the form: From the point of view of self-dqfusion, PUE phase falls into the anomalous bcc metals category (Tip , Hfp, Zrp, Uy) with a low-frequency factor and an activation energy lower than those provided by standard correlations. No theory proposed hitherto to explain these anomalies (influence of dislocations, of extrinsic vacancies bonded to inlpurities, of bi-vacancies) can clearly explain the self-diffusion coeffzcients of plutonium. DIFFUSION in bcc metals is a present-day problem. A recent symposium (Gatlinburg, 1964), followed by a book,' has been devoted to it. A great many experiments seem to show that diffusion in certain bcc metals obeys unexpected laws. The activation energies measured are sometimes strangely low (B hafnium, y uranium). For certain metals (0 zirconium, p titanium) the curves of log D (D = diffusion coefficient) as a function of 1/T (T = absolute temperature) are not linear. The frequency factors Do, which are of the order of 1 sq cm sec-' in fcc metals, vary from 1 to 10~6 sq cm sec-'. Various theories have been put forward to explain these anomalies; none is yet satisfactory. We wished to introduce a new experimental result by studying the self-diffusion in c plutonium. This allotropic phase, stable from 475°C up to the melting point (640°C), is in fact bcc. Unfortunately, nothing is known of the characteristics of the point defects in this phase, which limits the scope of the hypothesis which can be made about the mechanism(s) of self-diffusion in plutonium. 1) EXPERIMENTAL METHODS 1) Principle. We used the welded couple method. The two pellets of the couple initially have different 240 isotope contents (X emitter). After diffusion, the concentration/penetration curves are drawn up by the generalized Gruzin method. 2) Gamma Spectrography. The metal used in our study is plutonium, either low in puZ4O (isotopic content 1 pct) or high in puZ4O (8 pct). The latter also contains plutonium 241 (-1 pct) and 300 ppm of ameri-cium produced by the reaction Pu2U-AmM1 + 8-. The emission spectra of these two plutoniums placed in leak-tight vinyl bags have been studied by y spectrograph~. The detector is a thin crystal of thallium-doped sodium iodide. The activity of the plutonium rich in 240 is about twice that of the plutonium low in 240 in the energy band of 17 kev (L conversion lines of uranium); this band was used in these measurements. 3) Preparation and Examination of the Diffusion Couples. Diffusion couples were made from plutonium with a high and low PU"' content. Pellets (6 6 mm. thickness 3 mm) mounted on a polishing disc with ground parallel faces were polished mechanically on both sides. In this way, pellets with two parallel faces were easily obtained. The polished pellets were joined by a 6 phase anneal (420°C, 1 hr) in a small screw press (pressure of 20 kg per sq mm cold); a centering ring enabled the two pellets to be pressed coaxially. The couples then were subjected to the diffusion treatment by annealing in the E phase in sealed silica ampules in argon at atmospheric pressure. The annealing temperatures and times are given in Table I. The couples were encased in a mild steel ring, the joint interface being thus parallel to the ground face of the ring. The diffusion couple/ring assembly underwent successive abrasions by means of a magnetic plate grinder. The thickness of the abraded layer was measured with a Solex pneumatic comparator when it was less than 0.1 mm (accuracy 0.2 p) or with a mechanical micrometer (accuracy 3 p) for passes of the order of 0.2 mm. All these operations were done in glove boxes, as plutonium is particularly toxic. After each abrasion we determined the emission spectrum of the ground face. The emissive surface is defined by means of a diaphragm 3 mm in diam. We noted more particularly the X activity in the 17-kev

Jan 1, 1969

By P. Condori

Palabora Mining Copper has a unique ore body composition which unlike other copper ore bodies has three main components in significant proportions; these are copper bearing ore, magnetite and dolerite. The high content of dolerite, a hard barren material, creates a high proportion of pebbles which normally are recycled back to the mill. This action increases the mill bearing pressure and power progressively until corrective actions are taken. A logical action to solve the pebbles generation would be to incorporate a pebble crusher. This in fact was done however two fundamental issues were encountered; the high content of magnetite and existence of a cyclone classification section. Due to the high content of magnetite, metal detectors have not been able to work efficiently to separate tramp metal which causes damage to the pebble crushers. The existence of cyclones in the circuit had a detrimental effect on the final product when the pebbles crusher was online producing coarse sandy material. Due to the difficulties in treating pebbles via conventional procedures and the unique Palabora ore composition and characteristics, sorting technology was investigated at laboratory and pilot scale. It was found that a combination of optical and electromagnetic sorting could efficiently separate dolerite from the copper bearing and magnetite ores. This paper reports the findings of the laboratory and pilot scale work performed and discusses the additional benefits to the circuit.

Jan 1, 2012

By Hiroaki Kawamura, Takeshi Yoshikawa, Kazuki Morita, Yutaka Yanaba

"To develop an alternative metallurgical process for phosphorus removal in the production of solar-grade silicon (SOG-Si), slag treatment of metallurgical-grade silicon (MG-Si) was conducted, followed by acid leaching. Phosphorus-doped silicon alloy or MG-Si containing certain amounts of phosphorus and calcium was reacted at 1723 K and 1773 K with CaO--CaF2 of several compositions. Phosphorus removal from the molten silicon into the slag phase was confirmed by reduction to phosphide ions, P3-, and phosphate ions, P3-. These ions were separately determined using a wet chemical analysis method developed by ourselves. The highest phosphorus distribution ratio obtained was 2. 7 after reaction for 18 h with 17.5 mass% CaO--CaF2 slag. We then conducted acid leaching of the silicon and achieved removal of a large fraction (over 90 % ) of the phosphorus, which was much higher than that obtained by ordinary oxidizing slag treatment.IntroductionIn recent years, the production of solar cells has been increasing rapidly. Because of this, the demand for solar-grade silicon (SOG-Si) has also been growing rapidly. The development of lower-cost mass production processes is therefore needed to provide silicon feedstock. Phosphorus is one of the impurities in metallurgical-grade silicon (MG-Si). Because of its large segregation coefficient (kp = 0.35) [l ], it is difficult to remove phosphorus using a solidification refining process. Vacuum melting is considered to be a promising method for removing phosphorous from MG-Si [2], but the issues of high cost and large energy consumption have still to be resolved.Slag treatment is often used to remove impurity elements by oxidizing reactions during general oxidation refining processes. For example, phosphorus in molten steel is removed into a slag phase as phosphate ions, PO4 3-l-, by the following reaction:"

Jan 1, 2013

By Chas. F. Jackson

This paper is a tabular compilation of data contained in a series of information circulars dealing with mining methods and costs at a large number of mines in the United States and some foreign countries. There circulars have been published from time to time during the years 1929 to 1934 inclusive. From time to time, as enough data became available in these circulars, other circulars and. bulletins have been published in which the data bearing upon different phases of nine operation were summarized, discussed, and analyzed. The present paper is a compilation of data on costs of drifting and crosscutting contained in earlier circulars, .designed to assemble this information in a convenient form for reference without attempting lengthy discussion of details of drifting and crosscutting practice. For such details the reader is referred to the circulars on individual mines.

Jan 1, 1935

By P. E. Venteer

The Grootegeluk coal-processing plant treats 3 kt of raw coal per hour to produce a middlings fuel coal and a coking coal fraction with ash contents of 35 and 10 per cent respectively. The plus 0,5 mm fraction is treated by heavy-medium processes, the final top size of the coal being 15 mm. About 400 t of minus 0,5 mm coal per hour is subjected to froth flotation. The routes originally considered for the processing of this fine coal were froth flotation, shaking tables, heavy-medium cyclones, and water only cyclones in combination with froth flotation. The results from tests on the fines arising from a small-trial open-cast mine are discussed. When the froth flotation route was decided upon, further tests were conducted on the selection of the equipment most suited to the particular requirements of this coal and the rest of the plant. Tests using different types of flotation cells and dewatering equipment are discussed. During the commissioning, several operational problems were encountered, and the work done to find the best solutions is discussed.

Jan 1, 1984

By A. J. Barry

An apparatus and procedure have been developed for testing the anchorage effectiveness of slotted-type bolts. The apparatus consists of: (1) A hydrualic Jack assembly for loading the bolt and (2) a device (extensometer or cathetometer) for measuring displacement of the bolt as it is loaded. This apparatus and procedure permit measurment of anchor slip for loads up to the yield load of the bolt. Two representative makes of slotted-type bolts (a total of 94 bolts) were tested in typical sandstone and shale mine roof. Analysis of the test results showed that (1) anchorage capacities up to the yield load of the bolts can be developed in either rock type; (2) the shape of the slotted end of the bolt affects the ease with which the bolt can be driven; (3) all bolts for which the driving distance was more than 1.25 inches produced satisfactory anchorage in both rock types (thus, driving distance can be used as a criterion for satisfactory anchorage); (4) for the group of bolts that was satisfactorily anchored the anchor slip was unaffected by the type of bolt but was considerably larger in shale than in sandstone; and (5) the bolt expansion, that is, the amount the wedge expands the prongs in excess of the diameter of the hole, can also be employed as a criterion for satisfactory anchorage. Although the bolt-expansion and driving-distance results do not differ appreciably, the latter is recommended because it is easier to determine.

Jan 1, 1954

By Floyd M. Thorman

Gypsum is the crystalline chemical compound CaS04?2H20. A close chemical relation - and frequently occurring with Gypsum ? is Anhydrite which is Cask. Gypsun has wide commercial use because relatively simple heat processing reduces it to Plaster of Paris. While Anhydrite can be converted to Gypsum and thence to Plaster of Paris, the procedure is not simple and is quite costly. Anhydrite, however does have use in the agricultural field and in the Portland Cement industry. Occurrence of Gypsum in the earth structure is usually near or at the surface. Most underground mining is at 60 to 100 feet although one mine in southwest Virginia reaches a depth of 1300 feet. Gypsum is one of our softest minerals, rating only 2.0 on the Mohs scale of hardness. Specific gravity is 2.3 to 2.4. It is soluble in water but only slightly so. Interestingly, it is more soluble in cold water than in hot. For example, one part Gypsum dissolves in 370 parts water at 106° Fahrenheit while at 212°F. the water requirement is 452 parts. Compressive strength of massive Gypsum runs about 3000 lbs. per square inch. Color ranges from grey and brownish-grey to white.

Jan 1, 1973

Grade uncertainty can have a number of important implications for a mining operation. One of the most significant risks in not considering grade uncertainty in planning is the over or under allocation of processing or mining capacity when compared to realised grades. This could lead to wasted capital expenditure or missed opportunities to add value. This paper demonstrates a method that optimises production capacity and mining schedules in the presence of grade uncertainty. Applying this method to the case study of a nickel deposit recommended a reduction in processing capacity, an increase in mining capacity and more extensive utilisation of stockpiles than optimisations completed with traditional methods. As a result, average NPV improvements of between seven per cent and 27 per cent were gained.

Dec 6, 2010

By Jr. Loper, M. H. Kim, H. H. Jo, C. S. Kang, T. S. Song

"An investigation has been conducted to describe the effect of grain refiner (e.g.,Ti) or modifier (e.g., Sr) on the microstructure of an Al-11.3wt%Si alloy produced by the Ohno horizontal continuous casting process using a heated mold so as to obtain directional solidification at high cooling rate of 300 to 2000°C/s. Experimental results demonstrated that the directionality of the primary a grain was promoted by the addition of0.2 to 0.4%Ti or by the addition of0.02%Sr, whereas the addition of0.6%Ti suppressed this directionality. Feathery a grains were promoted by the addition of 0.2%Ti, while these feathery a grains were suppressed when over 0.4%Ti (grain refinement) or when 0.02%Sr was added. The addition of Ti also resulted in increased coarsening of the eutectic Si in these Al-1 l.3wt%Si alloys.IntroductionThe mechanical properties of conventionally cast Al-Si alloys can be enhanced through judicious control of the casting parameters, by the addition of grain refiners (e.g., Ti) and by the addition of eutectic modifiers (e.g., Sr).[1-3] The Ohno continuous casting process[4-5] uses a heated mold (maintained at a temperature above the alloy liquidus temperature) to produce a casting with a mirror surface free of shrinkage defects. The process is especially suitable for the production of high quality and non-deformable rods of small diameter. This study was conducted at investigate the effects of Ti and Sr on the microstructure of Al-1 l .3wt%Si rods cast by the 01).no process."

Jan 1, 1998

By Paul Javor

Optimization of a process is achieved by selecting, 'from all the known options, the most beneficial method of obtaining a product. It is rare that the optimum process is arrived at by conventional methods, because of the great amount of time required for developing and comparing all the options. On the other hand, it is now possible, by means of an optimization program based on special mathematical formulas involving an algorithm and implemented by a computer, to plot the optimum process realizing considerable savings and in a reasonably short time. The flow sheet arrived at in accordance with the optimization program described in this paper investigates and develops all the possible options and, with the aid of the computer, makes it possible to select the most economical ore beneficiation process. The options in an ore beneficiation process are all the possible trajectories that can be traced through the particle sizes to which the ore is reducible in the extraction of its valuable minerals. Although an ore can have a wide range of composition and several valuable minerals that can be extracted, this paper is concerned with the special case in which only one mineral is extracted from the ore and in which the maximum allowable percentage of impurities in the end product is defined.

Jan 1, 1971

By V. R. Garfias, H. J. Hawley

FoR a number of years the senior author has been interested in the various geologic and engineering problems involved in the development of the petroliferous districts of northeastern Mexico, having in a previous paper* endeavored to present a summarized statement of the information relating to the geology and soil resources of this region. Of the many interesting geologic phenomena, perhaps those which have been the object of most speculation relate to the igneous intrusions which, in places, have a controlling influence on the accumulation of oil in commercial quantibies, a relationship which has been tentatively explained by various observers with as many interestingly different views. The authors of the present paper aim to record, in the course of a general discussion of the various viewpoints, some additional data, and present further tentative conclusions with a view to rounding out an up-to-date summary of the subject. The greater part of the area in question lies in the State of Vera Cruz, only a northwest fraction being in the State of San Luis Potosi. Vera Cruz is bounded on the north by the State of Tamaulipas, the northernmost of the Mexican States along the Gulf. The topography of the States of Tamaulipas and Vera Cruz and of Texas and Louisiana to the north, is controlled by the Gulf coastal plain which in northern Vera Cruz has an average width of about, 60 miles, the transitional topography between that of the rugged Banks of the Sierra and the lowlands of the coast being made up of a series of terraces and irregular hills and valleys. Geology and StRucture The greater part of the mainland of Mexico is made up of Tertiary and later effusive rocks and of sedimentaries of Cretaceous age. The igneous rocks form a belt from 150 to 300 miles wide, spurs of which shirt

Jan 1, 1918