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SCIENCE 



[N. S. Vol. XXV. No. 631 



gists began the study of that western won- 

 derland. The earliest geological work was 

 done in connection with expeditions under- 

 taken for other purposes, as the Pacific 

 Railroad explorations, which commenced in 

 1853, and Ives's Colorado expedition. It 

 is, however, forty years since the national 

 government established geological surveys 

 in that western country. A period of a 

 dozen years commencing with 1867 was 

 marked by the achievements of four great 

 organizations devoted specifically to geo- 

 logical work — the Survey of the Fortieth 

 Parallel, the Survey West of the One 

 Hundredth Meridian, the Survey of the 

 Territories and the Survey of the Rocky 

 Mountain Region. Since 1879 all these 

 organizations have been superseded by the 

 United States Geological Survey. A new 

 world for geologists was that weird western 

 land— that land of deserts, plateaus and 

 caiions, with vast stretches of almost hori- 

 zontal stratification broken by faults and 

 monoclines, revealing its geological struc- 

 ture with wondrous clearness by reason of 

 an arid climate whereby it has been left 

 naked and destitute of any mantle of soil 

 and vegetation. There is revealed, as no- 

 where else in the world, the power and the 

 method of subaerial denudation. The 

 Grand Canon of the Colorado is a stu- 

 pendous object lesson of erosion; and, if 

 one is compelled to recognize river erosion 

 in the canon itself, scarcely less strenuous 

 is the compulsion to recognize subaerial 

 denudation in the vast platform of Car- 

 boniferous strata with little outlying buttes 

 of Permian and later formations. The 

 study of that country has been fruitful in 

 its contributions to the knowledge of aque- 

 ous agencies in dynamical geology. Very 

 early appeared those three monumental 

 works: Powell's 'Exploration of the Colo- 

 rado River,' Gilbert's 'Geology of the 

 Henry Mountains' and Button's 'Tertiary 

 History of the Grand Canon District.' 



The value of those early studies in a new 

 field is not greatly lessened if some conclu- 

 sions must be modified by later study. It 

 may be that the course of the Green River 

 through the Uinta Mountains is not a typ- 

 ical case of antecedent drainage; and it 

 seems certain that the esplanade in the 

 Kanab section of the Grand Canon is not 

 due to a long pause in the movement of 

 elevation, in which the river nearly at- 

 tained base-level: but the conceptions in- 

 troduced into dynamical geology as the 

 result of those early studies are no less 

 valuable and fruitful. 



The first lesson that geologists learned 

 in that western land was the efficiency of 

 subaerial denudation — the power of atmos- 

 phere, rain and river to remove vast quan- 

 tities of material, and shape the topo- 

 graphy of wide areas. From Hitchcock's 

 ' Elementary Geology ' I learned in my boy- 

 hood, in regard to cracks and fissures in 

 the strata, "If the fissure is open and of 

 considerable width, it is called a gorge; if 

 it be still wider, with the sides sloping or 

 rounded at the bottom, a valley is pro- 

 duced. ' ' Hitchcock was convinced, indeed, 

 that the Niagara gorge was due to erosion ; 

 but he declared that the gorges of the Con- 

 necticut between Mount Tom and Mount 

 Holyoke, and below Middletown, could not 

 be due to the action of the river, and that 

 the gorges of the same river at Bellows 

 Falls and Brattleboro were too wide to 

 have been formed by the river alone. In 

 his 'Illustrations of Surface Geology,' in 

 discussing the criteria by which to distin- 

 guish fluviatile from oceanic work, he de- 

 clared, "Rivers have little power to form 

 wide valleys." Apparently geologists were 

 confused with a vague idea that the ocean 

 is bigger than the rivers, and that, there- 

 fore, it can do more work in erosion. As 

 early as 1847, Ramsay had recognized that 

 the summits of the mountains of Wales 

 were remnants of a former plain of erosion, 



