Lyon Mountain deposits returned 10.86 per cent. Fe2O3, or 7.60 per cent. iron, of which 8.16 per cent. Fe2O3 was in the pyroxene mineral. On the basis of the mineral analysis of the gabbro it is reckoned that the three minerals-hornblende, hypersthene and magnetite making up 60 per cent. of the mass of the gabbrocontain by themselves 18.4 per cent. Fe2O3, but here a little error has crept in as the correct amount on the assumed basis would be 19.2 per cent. By deducting the iron in the form of magnetite it is concluded that the hornblende and hypersthene of the gabbro have lost much iron in conversion to diallage.

The figures afford little basis for a quantitative statement of the problem. So far as they go they indicate that the gabbro with 11.54 per cent. Fe2O3 may have been transferred to a diallage rock with 10.86 per cent. Fe2O3, but not much else. There is no information vouchsafed about the equivalent volumes concerned in the operation, or the material additions or subtractions which, if the theory is correct, must have taken place. But even admitting that the gabbro contains several per cents. of iron more than the diallage rock, which is scarcely indicated by the analysis, is the mass of the gabbro that may have been ingested in the granite proportionate to the effects produced in the formation of the magnetite deposits? That is the crucial point.

The general character of the gneiss or granite does not give support to the view that it has has absorbed large amounts of foreign material, except very locally. In the Palmer Hill district to the east of Lyon Mountain the rock is nearly a pure feldsparquartz-magnetite mixture, and in the writer's observation that is the prevailing character of it. Admixture with foreign material seems to have no bearing on the distribution of the ores in general, although in the Lyon Mountain district some of the deposits do align themselves more or less with the hornblende and mica schists enclosed by the granite. Palmer Hill and many other mines exemplify their association with granite notable for its small amounts of the dark minerals, except magnetite which not infrequently runs up to 10 or 15 per cent.

Dr. Miller himself does not seem to hold that the granite has

actually absorbed much of the gabbro, as he states that the typical rock is a microcline-microperthite-quartz material with only 8-10 per cent. of plagioclase in the form of albite and oligoclase. Consequently the abstraction of iron has been a sort of lixiviation process, without notable incorporation of the other ingredients. In any case it must be held that a very large body of the gabbro was involved, that the magmatic solutions penetrated it very thoroughly, that the iron so taken up was later segregated in order to form ores of 30-50 per cent. iron content in very substantial bodies. With such large masses the chilling effect upon the solutions would be considerable and tend to block the migration of the iron oxide. It seems likely that the iron must crystallize out close to the source of supply, so that the total effect would be one of dilution rather, through addition of the magmatic material.

Such theory also fails to account for the iron content of the granite in its normal phases. This is a matter that has not been dealt with, but it needs to be taken into consideration. In its mineral and chemical properties the rock belongs to the general type of soda-rich granites and syenites that have come to be known as the predominant magnetite-bearing rocks the world over. If segregation of the iron in the granite itself may not explain the formation of ore bodies like those in question, then our theories of magmatic processes appear inadequate.

The late crystallization of the magnetite particles which Dr. Miller notes in regard to the ores is not exceptional; also it is not necessarily indicative of a later introduction of magnetite after the crystallization of the silicates; rather it seems to depend upon the proportion of iron to the other ingredients. Thus in ordinary gabbro the magnetite or ilmenite normally crystallizes first but in the segregated ores it is the last to form.

The Precambrian magnetites present very intricate problems and their solution requires close study, such as Dr. Miller has given to the present occurrence. My criticism is that he has overemphasized certain features which really play a minor rôle in the ore-forming process.

ALBANY, N. Y.

D. H. NEWLAND.

REVIEWS.

The Copper Deposits of Ray and Miami, Arizona. By FREDERICK Leslie RANSOME. U. S. Geological Survey, Prof. Paper No. 115, 192 pages, numerous maps and illustrations. 1919.

This is the third great monograph on Arizona copper deposits by Dr. Ransome. It is shorter than the Bisbee paper, somewhat larger than the Globe paper, and ranks with them as a lucid treatment of a complicated area containing important mineral deposits. It is the first adequate treatment of the genesis of the disseminated chalcocite deposits in schists. Ray and Miami are located in central Arizona, about eighteen miles apart, in the belt of mountain ranges that borders the Arizona Plateau along its southwestern edge. To the end of 1918 they have yielded 1,098,409,607 pounds of copper, and the three principal mining companies have declared dividends amounting to $67,592,552, of which $8,548,050 was paid by the Inspiration Consolidated Copper Co. as a result of its first full year's operations, in 1916. Estimates give the ore originally present in the Miami district as 145,000,000 tons and in the Ray district as 115,000,000 tons. The tenor in copper ranges from about 1.5 to 6 per cent., and the average of the ore mined lies between 1.5 and 2 per cent.

The oldest rocks in the region are the Pinal schist, which consists mainly of metamorphosed siliceous sediments, and various granitic intrusives. All are pre-Cambrian. Resting on the eroded surface of these rocks are beds about 1,300 feet thick, supposed to be Cambrian. Above the Cambrian is 325 feet of limestone, probably Devonian. Above the Devonian is Carboniferous limestone, at least 1,000 feet thick.

After the deposition of the Carboniferous limestone, the region was uplifted and eroded. At about the same time diabase was injected into fissures in the older rocks, and from these fissures the magma was forced as sills between the beds, so that great masses of strata were driven apart and in places were completely enveloped in the igneous rock.

The intrusion of the diabase was probably followed by erosion and possibly by the deposition of Cretaceous sediments. The deposition of the supposedly Cretaceous beds was succeeded by andesitic eruptions. The andesitic eruptions were followed by the successive intrusion of (1) quartz diorite, (2) granite, quartz monzonite porphyry, and grano

diorite in masses, some of which, as the Schultze granite, are several miles in diameter; and (3) quartz diorite porphyry, in dikes and sills. The intrusion of the rocks of the second group was the cause of the original metallization that gave rise to the protores of Miami and Ray. The time of the intrusion of the rocks in these three groups is not known but is thought to have been early or middle Tertiary. Erosion followed, attended by deposition of the Whitetail conglomerate, which subsequently was buried under a flow of dacite. Later the Gila conglomerate was deposited.

Erosion attended by weathering and secondary enrichment altered. enormous bodies of low grade protore to workable copper ore. The ore bodies are flat-lying masses of irregular and more or less indefinite horizontal outline. The shape and size of each body depend largely upon the lower limit set for the percentage of copper in material classifiable as ore. Generally, the ore is overlain by leached, nearly barren rock known as capping, although in places the overburden contains considerable chrysocolla and malachite. The capping ranges from 40 to 1,000 feet in thickness. The average thickness at Ray, on the ground of the Ray Consolidated Copper Co., is between 200 and 250 feet. The ore grades downward into pyritic material that generally contains too little copper to be workable. The maximum is about 500 feet, but the average thickness of the Ray Consolidated Copper Co.'s ore body is 120 feet.

The ore bodies in a very general way have a marginal position with reference to intrusive masses of granite, granite porphyry, and quartz monzonite porphyry, but the ore occurs both in the schist and in the intrusive granitic or monzonite porphyry. The greater part of the ore is metallized Pinal schist.

From the relation of the ore bodies to the present surface, it is concluded that the greater part of the enrichment was effected before the development of the present topography and probably before the eruption of the dacite. As enrichment progresses and chalcocite increases the process of enrichment becomes slower in action, and erosion may, in some circumstances, overtake it.

Although much of the enriched ore is now below ground-water level it probably was once above that level, and enrichment is believed to have taken place mainly in the zone of rock above any general water table. If it is true that the enrichment was mostly earlier than the eruption of the dacite, it must, of course, have preceded also the laying down of the Gila conglomerate. This conclusion admits the possibility of the discovery of ore underneath certain areas of the conglomerate, particularly between Miami and Globe.

W. H. EMMONS.

SCIENTIFIC NOTES AND NEWS'

FRANK L. HESS, of the U. S. Geological Survey, sailed for South America, December 6.

CHARLES BERKEY, of Columbia University, has been making an examination of the Hill Top Metals Company's holdings in the Chiricahua Mountains, near Douglas, Arizona.

D. H. NEWLAND, Assistant State Geologist of New York, has a six months' leave, and is spending it in geological and mining work in the West.

NELSON H. DARTON, geologist of the U. S. Geological Survey, will spend two months early in 1920 in the Dominican Republic investigating oil conditions there.

A. G. MADDREN, formerly with the Alaskan Division of the U. S. Geological Survey, and with the U. S. National Museum, has entered the employ of the Vulcan Oil Company. He will make a detailed study of part of the Ranger oil field, in Texas, working under the direction of Dr. Ralph Arnold.

E. B. YOUNG, assistant in the Geological Department of the Anaconda Copper, and Secretary of the Montana Local Section of the A. I. M. E., is publishing in the Anode a series of articles on geology which are proving valuable to the non-technical men of the Anaconda Company.

J. VIPOND DAVIES has been elected president of the United States Engineering Society, succeeding Charles F. Rand.

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Geologists, mining engineers and others interested in applied geology are invited to keep the editor informed of new investigations of mining districts or scientific studies undertaken by them, together with such other scientific and personal items as may come to their notice.