Feb, 15, 1877] 



NATURE 



337 



THE UPPER COLORADO^ 



AMONG the most eminent services rendered by Ame- 

 rican geologists to the cause of science, there can 

 be little hesitation in placing the labours of Lieut. Ives 

 and Dr. Newberry as given to the woild in their well- 

 known Report on the Colorado country of the West. 

 By pen and pencil they brought vividly before the eye 

 and the imagination the structure and scenery of a 

 region so singular and so stupendous in its memorials of 

 slow prolonged subaerial erosion as not only to throw 

 every other known district of the kind far into the shade, 

 but to furnish proofs of the potency of river-excavation, 

 which even the keenest advocates for the power of rain 

 and rivers at first hesitated to believe. Since that Report 

 appeared, however, additional and confirmatory illus- 

 trations of the same marvellous scenery have been pub- 

 lished by other observers, notably by Hayden and Powell. 

 The gorges of the Colorado, with walls sometimes more 

 than a mile high and running for nearly five hundred miles 

 across the tableland, are now more or less familiar, from 

 descriptions and sketches, to the geologists of all 

 countries. They are admitted, too, to be due, as Dr. 

 Newberry first contended, to the gradual erosive action of 

 the rivers by which they are traversed. The whole of 

 this Colorado ba^in or plateau is justly regarded as the 

 most magnificent example on the face of the globe of 

 how much the land may have its features altered by the 

 agency of running water. 



In the present Report Dr. Newberry gives the results 

 of a second exploration to the Colorado, but to a more 

 northern or higher tract than that embraced in his previous 

 journey. The Expedition took place as far back as 1859, 

 and this Report was written and sent to the authorities 

 by the begin aing of May, i860. At that time, however, 

 the Civil War was impending, by which not only this 

 publication but many others of importance were arrested. 

 The recent surveys of the Department of the Interior 

 and the Bureau of Engineers having called renewed 

 attention to the Colorado region. Col. Macomb and Dr. 

 Newberry have succeeded, at last, in inducing the autho- 

 rities to print and circulate their account of the obser- 

 vations made by them seventeen years ago. It is a 

 welcome contribution to the literature of the subject. 

 Dr. Newberry, by his summary and his narrative of 

 detail, combined with his clever lithographic sketches, 

 presents us with so vivid a picture of the landscapes 

 through which he has wandered and of the geological 

 structure which has given them their character, that 

 nothing further can be desired save a personal visit to 

 the marvels themselves under his experienced guidance. 

 Four of the most characteristic views are here reproduced 

 as woodcuts. 



Westwards from the Rocky Mountain ranges to the 

 head of the Gulf of California the basin of the Colorado 

 stretches as a vast plateau, broken by the transverse gorge 

 of the Great Caiion, at the bottom of which, from 3,000 

 to 6,000 feet below the level of the plain, the river wan- 

 ders to and fro for nearly 500 miles. The plateau is further 

 marked by a succession of terraces ending in steep walls 

 somctunes 1,000 feet or more in height, and by occa- 

 sional isolated mountain areas which rise above the 

 general level like islands from the sea. These various 

 inequalities, however, when seen from any of the emi- 

 nences bordering the plateau are almost lost in the vast 

 sweep of the level plain. On all sides the table-land is 

 surrounded with mountain-ranges which seem .on the 

 whole to have a meridional direction, so that the table- 

 land itself would appear to be a tract which has somehow 

 escaped plication during the movements by which the 

 encircUng ridges were formed. The isolated mountains 



» Geological Report, by J. S. Newberry, M.D., of the United States 

 Exploring'Expedition under Captain J. N. Macomb, from Santa ¥6, New 

 Mexico, to the Junction of the Grand and Gieen Rivers of the Great 

 Colorado of the West. (Washii>gton, 1876.) 



on this plain, however, indicate the same north and south 

 trend, are composed like these bounding ridges, and may 

 be referred to the same series and to a similar mode of 

 origin. 



In that upper part of the Colorado plateau now de- 

 scribed by Dr. Newberry we recognise the same geologi- 

 cal formatlans as well as the same striking features of 

 colour which have given its name to the chief river. The 

 oldest rocks belong to the Carboniferous system. Thence 

 up to strata believed to represent the earlier Tertiary 

 series of Europe there is a continuous conformable 

 development of stratified deposits. These strata spread 

 out in horizontal sheets over the plateau. On the eastern 

 and western margins they have been heaved up along the 

 flanks of the mountain ridges, and here and there, where 

 an isolated axis of elevation or a dislocation occurs on 

 the plain, they have likewise been upturned. But for the 

 most part they retain their horizontality, so that the lower 

 formations are not seen, except where they have been cut 

 into at the bottoms of the caiions. The Carboniferous 

 limestones contain such characteristic brachiopods as 

 Productiis semireticulatus, P. scabriculus, P. punctaius, 

 Spirifer, and Athyris. The earliest records of that 

 region, therefore, are those of a sea- floor, which must 

 have stretched eastwards across what is now the range of 

 the Rocky Mountains towards the land which then lay 

 over the site of the Eastern States. The thickening out 

 of the marine limestones towards the west establishes 

 this point in the ancient physical geography of the Ameri- 

 can continent. Above the Carboniferous limestones and 

 shales lie a conformable series of bright red, green, and 

 yellow sandstones, shales, and marls, which are regarded 

 by Dr. Newberry as Triassic, and perhaps partly Jurassic, 

 and which pass conformably upward into massive yellow 

 and grey sandstones and green shales, which are placed 

 on the horizon of the Lower Cretaceous rocks. These 

 latter strata, containing many cycads and ferns, with 

 other traces of terrestrial conditions, form the surface 

 over an enormous area of the table-land. As they ap- 

 proach the broader valleys they end ofif in a steep cliff or 

 blutf like a sea-wall, often cut along the edges into nume- 

 rous detached tables, pinnacles, and quaintly-shaped out- 

 liers. The red strata underneath form the platform out 

 of which the deep gorges have been eroded and their 

 bright colours running in parallel stripes along the walls 

 of the caiions and the faces of the isolated fragments and 

 pillars give an extraordinary character to the fantastic 

 forms into which the rocks have been worn. 



The want of any evidence of disturbance from palaeo- 

 zoic up into older Tertiary time is dwelt upon by Dr. New- 

 berry in this Report as showing the simplicity of the struc- 

 ture of this part of the continent. The facts which he brings 

 forward help to make our ideas still' clearer of the stages 

 by which the present physiography of America has been 

 reached. He demonstrates the truth of his previous con- 

 clusion that the region of the Colorado is one of vast 

 erosion, and he gives some interesting indications of the 

 extent of this denudation. He shows that the great plain 

 with its surface of firm Lower Cretaceous sandstone was 

 once covered by a continuous sheet of soft Middle and 

 Upper Cretaceous shales, of which scattered mounds and 

 millions of loose fossils are strewn over the plain, and 

 which rise along its margin into an upper plateau over- 

 looking the great tableland and presenting a steep escarp- 

 ment towards it. These overlying strata are at least 

 2,000 feet thick. There cannot be any doubt, therefore, 

 that previous to the erosion of the profound gorges the 

 tableland was buried under 2,000 feet of soft strata, all of 

 which have been removed except these fragmentary relics. 

 Dr. Newberry satisfactorily disproves the notion that this 

 denudation could have been effected by any violent cur- 

 rent like those waves of translation which used to be 

 called in to account for the existence and distribution of 

 the glacial drift and erratic blocks. No one can read his 



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