NATURE 



{Nov. 4, 1875 



graphically and geologically, an area of 5,600 square 

 miles during the period between the end of May and the 

 latter part of October ; the third division, under Dr. 

 F. M. Endlich, accomplished the survey of nearly 7,600 

 square miles, "particular attention being paid to the 

 agricultural and mineralogiqal resources of the country 

 traversed." Allowing 130 full working days for the 

 period during which these two parties were at work, we 

 find that on an average 100 square miles were surveyed 

 topographically and geologically each day, and that this 

 was performed by some seven or eight observers ! And 

 if it be further noted that only half of that number were 

 geologists, and that in the case of the San Luis, or third 

 division, the geological work appears to have been done by 

 one man, we shall form some notion of the rate at which 

 scientific surveys advance in the far West. We have not 

 the same precise statements of the area actually surveyed 

 by the second or South Park division, under Dr. A. C. 

 Peale ; but it seems to have been on the same extensive 

 scale. 



Now by those who take interest in the progress of 

 topographical and geological surveying some explanation 

 will naturally be required as to the almost incredibly large 

 area examined in one season by Dr. Hayden's corps. 

 Compared with his rate of progress, our Ordnance and 

 Geological Surveys creep on at a snail's pace. His 

 geologists, for instance, get over in a single day an 

 amount of ground which the most hard-working and 

 experienced members of the Geological Survey of Great 

 Britain couldl hardly accomplish in a year's campaign. 

 Evidently the two kinds of work cannot properly be com- 

 pared with each other. That of the British Surveys is 

 minutely detailed, and meant to be, for the time, exhaus- 

 tive. The American Survey of the Territories, on the 

 other hand, cannot be regarded as, and does not pretend 

 to be, more than a rapid but intelligent reconnaissance, 

 ■wherein the positions of the leading landmarks are cor- 

 rectly determined, and those of the intermediate features 

 are fixed as nearly as may be ; while, acting in concert 

 •with the topographer, and availing himself of the same 

 points of observation, the geologist ascertains the nature 

 and order of the rocks in a few traverses from which he 

 infers what must be the structure of the surrounding dis- 

 tricts. It is no disparagement to this work to say that it 

 must in the end be superseded by more accurate and 

 detailed surveys. It is in the meanwhile doing a notable 

 service by pioneering in vast and unknown or little known 

 regions, and giving the world a first outline'of the main 

 features of their geography and geology. In the territory 

 of Central Colorado investigated in 1873, the geologists 

 had the advantage of comparatively simple structure to 

 deal with. So clearly does the skeleton of the continent 

 protrude in that region through the surface, that from each 

 main hill-top it was not difficult to follow for many miles 

 on successive ridges and spurs the crags and hollows 

 marking the lines of outcrop of particular strata. The 

 extent to which this peculiarity and simplicity of geolo- 

 gical physiography has been useful, may be inferred from 

 the numerous diagram-sections of the belt of country sur- 

 veyed, showing the relation of the surface-contour to the 

 arrangement of the underlying rocks. 



Space cannot be given here for a detailed account of 

 this Report, but reference may be made to some of its 



features which have a general interest. Mountain-struc- 

 ture, especially in relation to the plications of the crust of 

 the earth, receives much notice from the various mem- 

 bers of the Survey. They have followed the gradual 

 swelling pf the flat formations of the plains, first into gentle 

 ridges or " hog backs," then into more marked and 

 crested ranges, until they have traced them in vertical or 

 even inverted masses reposing against the central core of 

 granite. Crossing this latter they have caught up again 

 the same formations on the other side, and followed them 

 in like order and position from the disrupted and highly- 

 inclined central mass down to their gradual subsidence 

 into the flat plains. The rocks next to the granite are 

 metamorphosed, and, what must strike European geo- 

 logists as curious, have huge intercalated sheets and dykes 

 or veins of trachyte associated with them. The elevation 

 of the mountain ranges has upraised cretaceous rocks, 

 and even some parts of later geological formations. 



The length of time, however, which has passed since 

 the upheaval of the Rocky Mountains and their subsidiary 

 spurs has allowed a vast amount of work to be done upon 

 their slopes and crests by the weather, rain, torrents, 

 frost, snow, and glaciers. It would seem hardly possible 

 indeed to find a region where it would be more easy to 

 appraise exactly the amount of waste from a given area 

 due to this cause. The geological structure of the anti- 

 clinal and synclinal folds is so simple, the rocks are so 

 well exposed, and the limits of sub-aerial erosion seem so 

 sharply marked off from those of subterranean move- 

 ment, that the flanks of the Rocky Mountains might be 

 selected as a typical region for the study of this branch 

 of physiographical geology. Sometimes the corries or 

 cirques (" gulches " is their American name) have been 

 cut back so as to leave a steep hardly-traversible crest 

 between them, while now and then a valley has been cut 

 completely across the watershed, so as to draw its first 

 waters from the other side. In some places the rocks 

 have been so weathered as to stand up in extraordinary 

 pillars and capped statuesque masses like those for which 

 Saxon Switzerland has been so long famous. 



The former presence of extensive glaciers descending 

 from the mountains of Colorado has been proved by the 

 evidence of huge moraine mounds, admirable ice-worn 

 domes of granite, and scattered glacier-lakes. It would 

 seem, indeed, that no very great diminution of tempera- 

 ture might suffice to restore glaciers to these valleys. 

 Dr. Hayden describes vast masses of snow and ice, 

 which, melting in summer on the steep slopes and satu- 

 rating the rocks and soil, slide down like glaciers and 

 cumber the declivities and valleys with piles of rubbish. 



The now well-known geysers of the Yellowstone region 

 have made known the extent and comparative recentness 

 of volcanic action in that region. We learn some further 

 facts of interest on this subject from the present report. 

 Dykes and streams of basalt have been found in proximity 

 to their parent cones. In some cases the lava beds form 

 the cappings of isolated hills, or project as terraced bars 

 from the sides of the slopes. In other instances they 

 occur in the bottoms of the valleys, and even appear to 

 have sometimes crossed the present river-courses and 

 formed lakes. Recent, therefore, though these lava-erup- 

 tions must be, they were evidently continued during a period 

 of time long enough for deep and wide valleys to be cut 



