6oo 



NA TURE 



[April 19, 1900 



NORTH AMERICAN GEOLOGY. 

 "T^HE publications of the Geological Surveys in the United 

 *- States and in Canada are not e worthy for the exhaustive treat- 

 ment, from an economic as well as from a scientific point of view, 

 of the subjects dealt with. In dimensions, in type, and in wealth 

 of illustration, the numerous volumes which are issued bear 

 favourable comparison with works published elsewhere. 

 Reports of United States Geological Survey. 



Attention was called in Nature of June 22, 1899, to Parts 

 ii. and v. of the "Eighteenth Annual Report of the U.S. 

 Geological Survey." We have lately received Parts iii. and iv. 

 of the same Report. Part iii. is a bulky volume of 861 pages, 

 which relate almost wholly to economic geology. Mr. George 

 F. Becker deals with the gold-fields of Southern Alaska, while 

 Mr. J. E. Spurr and Mr. H. B. Goodrich contribute an elaborate 

 report on the geology of the Yukon Gold District, in the same 

 territory. To the last-named work special reference has already 

 been made in Nature (December 7, 1899, p. 124). The 

 Yukon gold-field lies close to the British frontier ; that of 

 Southern Alaska, to which we now draw attention, fringes the 

 coast from Sumdum Bay westward as far as Unalaska, the 

 mines being partly on the mainland, partly on islands. 

 Mr. Becker gives an account of the volcanic activity and changes 

 of level which have affected the region. Volcanic eruptions 

 have occurred in comparatively recent times, and the belt of 

 activity seems to have existed since late Eocene or early Miocene 

 times. The author describes the various eruptive rocks, and a 

 few schistose rocks which appear to be altered eruptive rocks ; 

 he also contributes notes on glaciation. The ore-deposits occur 

 in a belt which coincides with the planes of schistosity in the 

 altered rocks, and it is considered that their origin is connected 

 with eruptive phenomena. The minerals associated with the 

 gold are quartz and pyrites, copper pyrites, galena, zinc-blende, 

 &c. The author gives accounts of the mines, and of the placer 

 deposits, and refers also to certain auriferous beach-deposits. 

 At present the district is but imperfectly explored. 



Mr. Bailey Willis reports on some coal-fields of Puget 

 Sound, Washington. The coal-bearing formation (Puget 

 group) is of Tertiary age ; the lower beds being Eocene, while 

 the upper beds may be Miocene. The prevailing rocks are 

 sandstones, but the deposits vary from arkoses, consisting of 

 slightly washed granite materials, to siliceous clays, and they 

 contain much carbonaceous material and distinct coal-seams. 

 These strata rest unconformably on metamorphic schists and 

 limestones of Carboniferous and Jura-trias date, and they are in 

 places overlain conformably by marine Miocene (Tejon) strata. 

 Tertiary eruptive rocks of younger date are associated with the 

 Puget group. They occur as dykes and flows in various forms 

 of intruded and extruded igneous rocks. Glacial deposits extend 

 over large areas. The Puget strata were deposited in marshes 

 and shallow-water areas, and subsequently were subject to con- 

 siderable disturbances which led to folding and over-thrust, 

 followed by normal faulting. Variations in the quality of the 

 coals is attributed to the pressure and movement which they 

 have suffered. The coals range in character from lignites to 

 what are termed bituminous lignites or steam coals, and bitu- 

 minous coking coals. 



The geology and mineral resources of the Judith Mountains 

 of Montana, form the subject of a report by Mr. W. H. Weed 

 and Mr. L. V. Pirsson. These mountains are one of the groups 

 of the Great Plains of the North-west, the nearest peaks of the 

 Rocky Mountains being thirty-five miles to the west. They rise 

 like a great island above the plains to a height of about 2500 

 feet above this level platform, the most elevated peak being 

 6386 feet above the sea. Geologically the mountains have 

 been formed by a number of independent, coalescing, dome- 

 shaped uplifts, involving the sedimentary series from the Cam- 

 brian to Cretaceous, and they are penetrated by laccolitic and 

 other intrusions of igneous rocks. It is remarkable that while 

 the great series of sedimentary rocks is apparently conformable 

 throughout, yet the earlier strata are steeply upturned along 

 the flanks of the Rocky Mountains, and the disturbances die 

 out eastwards over the area of the plains. No Permian or Trias 

 sediments occur, and the region was probably a land-area during 

 those periods. Descriptions are given of the Cambrian, Silurian, 

 Devonian, Carboniferous, Jurassic and Cretaceous rocks, and 

 of the numerous laccolitic intrusions which are all of acid type. 

 Granites, syenites, diorites and nephelite-syenites are found, 

 the latter being represented by rocks of phonolitic character. 



NO. 1590, VOL. 61] 



The ore-deposits (chiefly gold) and the Cretaceous coal are 

 described. 



Mr. Waldemar Lindgren furnishes an account of the mining 

 districts of the Idaho basin and the Boise ridge, Idaho, with 

 a report on the fossil plants of the Payette formation, by Mr. 

 F. H. Knowlton. The region includes a portion of the lower 

 Snake River Valley and adjacent mountains on the northern 

 side, together with the entire drainage of the Payette, Boise, 

 and Wood rivers. The Boise mountains attain elevations of 

 over 7000 feet. The area consists largely of granite together 

 with the " Snake River Tertiaries." These latter comprise 

 early Neocene (Miocene) lake-beds, known as the Payette for- 

 mation, with which are associated vast masses of basalts and 

 rhyoHtes ; and later Neocene (Pliocene) deposits together with 

 the Snake River basalts. Sands and gravels of Pleistocene age 

 also occur. Gold occurs in the granitic rocks or associated dykes 

 and veins, and in placer deposits. Monazite is found in the 

 sands of the lake deposits, and there is no doubt that it forms 

 one of the original constituents of the granite of the Idaho 

 basin. This mineral, which is a phosphate of the cerium metals 

 and thorium, yields products of economic value in the preparation 

 of incandescent gas lights of the Welsbach and other burners. 

 Silver-ores also occur in the region. 



A preliminary report on the mining industries of the Telluride 

 Quadrangle, Colorado, is contributed by Mr. C. W. Purington. 

 This is a region of striking topographical features, the mountains 

 rise to over 14,000 feet, while some of the streams have cut pre- 

 cipitous channels in the mountain cirques or basins to a depth 

 of 7500 feet. Telluride, a town of about 1500 inhabitants, 

 is in the heart of the mining district. The first prospectors 

 entered the region about twenty-five years ago, and the district 

 has made a steadily increasing output from its discovery to the 

 present time. As remarked by the author, it has been the 

 history of many ore-producing regions that much more money 

 has been expended in the mining (and we might add financial) 

 operations than has been extracted from the ore taken out. 

 The Telluride district is said to be emphatically one where the 

 money value,represented by the labour and capital expended, has 

 not equalled or even approached in amount the product of the 

 mines in the precious metals. The lesson that is taught is that 

 conservatism in mining is poor policy, and that new methods and 

 devices to meet new conditions, for which no rules can be laid 

 down, are necessary for the successful production of ore in 

 newly exploited areas. The district is composed of nearly flat 

 sedimentary beds, which rest on Archsean and extend in geo- 

 logical age from the Trias to the Tertiary. This vast series 

 has been in places tilted up, deformed, injected and broken 

 through by igneous rocks, of Tertiary or Post-Tertiary age. 



The ridges of the mountains present exceedingly irregular, 

 sharply cut and jagged lines, whose sharp gaps are generally 

 the result of the more rapid weathering and wearing down of 

 metalliferous veins and zones of mineralised rock. Such zones 

 usually have most brilliant colours — red, white and yellow — and 

 are visible across country for a distance of twenty miles. With 

 regard to the scenery in general, it is remarked that the beauty 

 of form and colouring is unsurpassed in the mountain regions of 

 the world. The metalliferous portions of the rocks are thus 

 largely exposed to view, and their origin is attributed to the 

 subterranean tract from which the igneous rocks have come ; 

 surface waters having descended through fissures to the horizon 

 of the heated magma, and having subsequently ascended heavily 

 charged with mineral matter. The vein-filling is considered to 

 be later than the newest lavas exposed in the region. The vein- 

 deposits are valued chiefly for the gold and silver, while much 

 gold in a finely divided state occurs in placer deposits. It is 

 noteworthy that none of the tellurides or other possible rare 

 compounds of gold occur in the area, so far as the present 

 investigation has been able to determine. No silver- ore occurs 

 which does not contain, in the free state, more or less gold ; 

 while the galena, considered as an ore of silver, is merely the 

 gangue or mechanical matrix of gold. 



Part iv. of the "Eighteenth Annual Report" deals entirely with 

 hydrography. It is a huge volume of 756 pages, comprising 

 (i) Report on the progress of stream measurements for 1896, 

 by A. P. Davis ; (2) The water resources of Indiana and Ohio, 

 by F. Leverett ; (3) New developments in well-boring and 

 irrigation in South Dakota, by N. H. Darton ; and (4) Water 

 storage and construction of dams, by J. D. Schuyler. Among 

 the matters discussed is the temperature of the deeper artesian 

 waters in the Dakota basin. 



