5i6 



NATURE 



[Sept. 12, 1878 



the evidence, only known to himself, is or is not conclusive 

 to him, to introduce it as undisputed fact in this manner 

 in the present publication. After this we have not 

 enough interest to read the remainder of the book, and 

 besides it is so full of mistakes, as Urus for Ursus (p. 505), 

 shorter for longer (p. 511), &c., that it is a wearying effort 

 to understand in places what the author really means. 



J. S. G. 



AMERICAN GEOLOGICAL SURVEYS 



Geological and Geographical Atlas of Colorado and 

 Portions of Adjacent Territory. By F. V. Hayden, 

 U.S., Geologist in Charge. (Washington : Published 

 by the Department of the Interior, 1877.) 



IN the magnificent Atlas just issued by the Department 

 of the Interior v/e have the consummation and 

 crown of all the labours which Dr. Hayden and his staff 

 have carried on so triumphantly for the last five years, 

 and of which they have already given us so much in- 

 teresting and important information in a series of Annual 

 Reports. Before examining the work from a scientific 

 point of view, no reader can refrain from expressing his 

 admiration of the style in which the Atlas has been pro- 

 duced by the United States Government. As a specimen 

 of cartography, typography, and lithography, it is alto- 

 gether worthy of the highest praise. For beauty and 

 indeed sumptuousness of execution, it may be classed 

 with those livres de luxe which from time to time have 

 been issued from the National Imprimerie of France. 



The Atlas consists of two series of maps, the one of a 

 general, the other of a detailed kind. The first series, on 

 the scale of twelve miles to one inch, comprises four 

 sheets, each embracing the whole State of Colorado and 

 part of the neighbouring territory. The first of these 

 illustrates the system of triangulation adopted in the 

 survey ; the second shows the drainage system of the 

 area; the third by a simple and clear arrangement of 

 colours, exhibits at a glance the economic features of the 

 AYhole region — the agricultural land, pasturage, forests, 

 and woodlands, sage and bad lands, mineral tracts, and 

 the portions rising above the limit of timber-growth ; 

 the fourth contains a condensed and generalised geo- 

 logical map of the same territory. Nothing can surpass 

 the lucidity of expression and artistic finish of these 

 maps. 



The second series — twelve in number — is on the scale 

 of four miles to one inch, and consists of six topo- 

 graphical sheets and six identical sheets, coloured 

 geologically. The topographical details, though nume- 

 rous, are so selected as not to neutralise each other, or 

 mar the broad, clear picture which the maps were de- 

 signed to be. By means of contour-lines of 200 feet 

 vertical distance, the surface-configuration of the whole 

 region is depicted as in a model. We can follow the 

 lines of the broad valleys, of the deep, narrow canons, 

 and of the hundreds of minor tributaries which have 

 scarped out their courses on either side. Here we look 

 down upon a vast table-land, deeply trenched by stream- 

 channels ; there upon a succession of bold escarpments 

 or mesas which bound the table-land and hem in the 

 neighbouring valley. Huge mountain-ranges rising out 

 of the plateaus are so vividly drawn that they seem to 



stand out of the paper. Yet no shading is employed. 

 All the effects of inequality are produced by contour- 

 lines, so faithfully set down that a single line may be 

 tracked in its sinuous course along the whole of a moun- 

 tain front until it comes out upon the table-land beyond. 

 When will our map-makers learn to use this, the only true 

 method for expressing the surface of a country? The 

 best of our atlases are disfigured by strips of shading 

 running across the map like so many caterpillars, to 

 represent mountain-ranges. Even our Ordnance maps, 

 so admirable in most respects, are sometimes so loaded 

 with shading, that a steep hill-side only a few hundred 

 feet high is made as black as our highest mountains, and 

 the topographical names can hardly be read, even with a 

 magnifying-glass. 



But, above all, welcome are these six geological maps. 

 In the previously published maps and charts accompany- 

 ing the Annual Reports, only small detached areas were 

 represented, and even from the careful descriptions of the 

 various geologists of the staff it was hardly possible to 

 frame a satisfactory conception of the geology of Colo- 

 rado as a whole. Ever since the marvels of its deep 

 gorges and vividly painted cliffs were made known, that 

 region has possessed a high interest to the geologist. 

 He has now the means of gratifying his desire for further 

 knowledge. With the help of these maps and the two 

 accompanying sheets of sections he can realise most 

 satisfactorily every great feature of Colorado geology. 

 The ancient Archaean ridge — the nucleus or back-bone of 

 the American continent — may be traced running north 

 and south nearly along the present hydrographical axis 

 of the country. Flanking that ridge comes a series 

 of palaeozoic deposits, the oldest of which have been 

 identified palaeontologically with Silurian formations. 

 Rocks, regarded as of Devonian age, overlap the 

 Silurian beds, and repose against the ancient crystal- 

 line ridge on the south-west side of the San Juan 

 Mountains. They are soon buried under later accumu- 

 lations, and they seem to be of but local development, 

 since in most places where the rocks are found in 

 juxtaposition, the Silurian are directly succeeded by 

 Carboniferous strata. These last-named rocks cover 

 large tracts of country, running as bands round the 

 Archzean area, and lying in basins across it. Far to 

 the west where the Grand River has so deeply trenched 

 the Utah plateau, the flat Carboniferous beds appear from 

 under the brilliant red Triassic strata. The difficulty of 

 drawing any line between Triassic and Jurassic formations 

 in that region is again acknowledged on these maps, the 

 lower red series being doubtfully assigned to the older, 

 and the upper variegated deposits to the later system. 

 Cretaceous rocks are abundantly developed, and cover a 

 vast extent of territory. In particular they spread over 

 the wide plateaux between the San Juan and Gunnisen 

 rivers, and form the platform on which the enormous 

 volcanic outbursts have been piled up from the West Elk 

 Mountains southward into New Mexico. It is more easy 

 to trace on these maps, too, the area respectively occupied 

 by the Laramie, Wahsatch, Green River, Bridger, and 

 Uintah formations which represent post-cretaceous and 

 tertiary times. Glacier moraines, lake-deposits, drifts, 

 sand-dunes, and recent alluvia, all find adequate ex- 

 pression on the maps. Especial care, too, seems to have 



