282 



NA TURE 



[July 23, 1908 



GEOLOGICAL WORK IN THE UNITED 



STATES. 



^pHE work of the Geological Survey of the United States 



is in many regions also geographical. Bulletin No. 



307 (1906), by Henry Gannett, is thus a useful " Manual 





hlt_, I. — W'eaihenng ot iMadI^o[l vL-arbonilerous) J.iiiic-iinic. J Lju^ut Ki\cr 

 Canyon, Bighorn Mountains. 



of Topographic Methods," reviewing in its eighty-six pages 

 " the most approved methods of surveying a?, applied to 

 the production of topographic maps." 

 Those of us who have used the 

 American maps on the scale of 

 I : 62,500 may have wondered at the 

 selection of this figure in place of our 

 1 : 63,360, or I inch to one mile. It is 

 here clear, however, that the -American 

 scale is a convenient, deduction from 

 I : 250,000, which is employed for the 

 maps of large areas, and which fur- 

 nishes a scale of practically four miles 

 to an inch. The thick Bulletin No. 

 299, by Mr. Jas. McCormick, is a 

 second edition of the " Geographic 

 Dictionary of Alaska," and includes 

 9300 names, as against 6300 published 

 in 1902, numbers that afford " a rough 

 indication of .Alaskan growth." 



Mr. N. H. Darton's " Geology of 

 the Bighorn Mountains " (Professional 

 Paper No. 51, 1906) is a fascinating 

 description, very handsomely illus- 

 trated, of a region in Wyoming that 

 has come into notice as a summer 

 resort. There are few areas more 

 calculated to convert the ordinary man 

 into a keen stratigraphical geologist. 

 Huge sections can be read off on 

 the mountain-sides, and Cambrian, 

 Ordovician, Carboniferous, Triassic, 



Jurassic, and Cretaceous deposits are represented. The 

 Cretaceous system closes with fresh-water stages some 



XO. 202 1, VOL. 7S] 



9000 feet thick, containing coal-seams in the upper layers, 

 which correspond with tne type of strata usually known 

 as Laramie. Prof. R. D. Salisbury (pp. 71-90J describes 

 the glacial geology, largely from material gathered by 

 .Messrs. Blackwelder and Bastin. Two Glacial epochs are 

 traceable, and diminutive glaciers belonging to the later 

 one still remain in the great chain of pre-Cambrian 

 granite, rising 12,000 feet above the sea (see Plates xxix., 

 x.xxvi., &c.). It is claimed that glacial erosion has 

 deepened some of the valleys by at least 700 feet. A 

 glacial and a geological map accompany the memoir, in 

 a pocket at the end, in accordance with the convenient 

 plan now adopted by the United States Survey. 



West of the Bighorn Mountains stretches the Bighorn 

 Basin, on an average 5000 feet above the sea. Its geology 

 and water-supply have been described by Mr. C. .A. Fisher 

 (Professional Paper No. 53, 1906). The basin is formed 

 by a broad synclinal of the older strata, and its floor is 

 occupied by Laramie beds, unconformably covered by the 

 Eocene \\'asatch clays and sandstones, as is well shown 

 in Plate x. The ranges on the west divide this basin from 

 the 'Yellowstone Park, and hot springs and geyser-deposits 

 occur within the area now described. 



Mr. N. H. Darton, the author of the memoir on the 

 Bighorn Mountains, also describes the Arkansas Valley 

 in eastern Colorado (Professional Paper No. 52, 1906). 

 This is a dry region, where artesian water, held up in the 

 Dakota sandstone, is of great economic importance, and 

 the coloured map forming Plate xxvi. shows, by contour- 

 lines, the altitude of the top of the sandstone above sea- 

 level, whether exposed at the surface or concealed. The 

 uplift of the Rocky Mountains in this region followed on 

 the fresh-water Laramie epoch, and the rivers began to 

 form flood-plains, and to carve out the main features of 

 the topography in the western hills, as far back as Eocene 

 times (p. 49). The flat alluvial fan of Miocene age attains 

 in itself a thickness of 1000 feet. 



Mr. A. C. \'ea'tch's memoir on northern Louisiana and 

 southern .Arkansas (Professional Paper No. 46, igob) covers 

 a vast region, where the streams pour down from the 

 " wolds " on the Texas and Arkansas border into the 

 great alluvial valley of the Mississippi, which is rich in 

 " ox-bows," on the east. The characteristic Cretaceous, 

 Eocene, and Oligocene fossils are well illustrated, and 

 marine conditions remained in this area until a very 

 gradual tilting up of the north and a lowering of the 

 coast-region set in at the opening of Miocene times (p. 44). 

 The low mounds of fine loam, 20 feet to 100 feet across 

 and 3 feet to 5 feet high, which dot the fluviatile plains 



jLLirr iti ci'que. Cloud Peak, Bighorn .Mounlains. 



of the Louisiana and Texas coast, provide a very interest- 

 ing discussion (p. 55). They are not forming under exist- 



