ACADEMY OF SCIENCES] GILBERT'S WORK 289 



LIBERATION FROM WASHINGTON 



After 1S92, the disaster year of the survey, Gilbert was liberated from administrative duties 

 in the Washington office and was assigned, as now seems unfortunate, for three years, to a real 

 work on geological formations and underground water in Colorado. As such work was largely 

 of a standardized kind, of which any quantity could be done as it were to order by a standard 

 geologist, it contrasted with many of his other studies, which were so novel in ideas and methods 

 that he alone could carry them through. Hence here, as in his work on Bonneville and on the 

 Appalachians, he had the aid of assistants. His report, published in 1896, has more of a per- 

 functory quality than any other of his publications. This Colorado work will probably be 

 remembered not so much for the Pueblo folio which he and his assistants colored, as for his 

 new interpretation of the fresh-water Tertiaries of the plains as fluviatile instead of as lacus- 

 trine deposits; and for his views on " Rhythms and geologic time," which may be long in matur- 

 ing, but which seems destined to find important application. It was in connection with the 

 field work in Colorado that Gilbert became interested in the chemical composition of shales 

 and fire clays, of which a number of analyses were made at his request; but as usual this line 

 of laboratory research was not carried far. 



The physiography of Niagara and the Great Lakes again took his attention as soon as his 

 task in Colorado was completed, and results of increasingly quantitative character were soon 

 reached, along with many novel explanations of local features of glacial origin. Among the 

 latter the cross-spur channels in the district about Syracuse, N. Y., with their dry cataracts 

 and their plunge-pool lakes, deserve special mention as having afforded appropriate exercise 

 for his power of original interpretation; for although they are matters of small magnitude they 

 are of great theoretical import. The ingenuity of their treatment was truly Gilbertian. The 

 appreciation then gained of the importance of glacial erosion in shaping the landscapes of 

 western New York was a good prelude for studies of much more intense glacial erosion in Alaska 

 in 1899, and a few years later in the Sierra Nevada. It is noteworthy that in each of these 

 three regions the evidence discovered in favor of strong glacial erosion was of a purely physio- 

 graphic kind; that is, it was not based on a study of the physics of ice, or upon the nature of 

 glacier motion, or upon the volume of glacial drift, but directly upon the forms of the glaciated 

 land surface; for to Gilbert's anatytical mind every land form must have a responsible cause, 

 and to his expert eye the cause was declared by the form. The geodetic problem of isostasy 

 also engaged his attention in the nineties, and gave play to his spirit of philosophical inquiry as 

 well as to his capacity for mathematical discussion. 



It has been remarked that Gilbert was not of a reminiscent nature; he seldom talked of 

 his past experiences and he never wrote of them, and the world is therefore the poorer. Even 

 the contributions that he made to memorials of his chief, Major Powell, tell little about matters 

 that were not relatively well known to the geological public, although it can not be doubted 

 that the long intercourse between Powell and Gilbert would have furnished a large fund of 

 interesting stories concerning the development of the national survey; but narratives of that 

 sort do not seem to have appealed to him. As to his own more personal experiences he left 

 no records; he left untold even so adventurous an excursion as Wheeler's boat party in the 

 Colorado Canyon. It is probable that few persons ever heard him mention it. He was a for- 

 ward-looking student of nature; his 'own part in his studies was seldom referred to. 



WORK IN CALIFORNIA 



GUbert's brief return to the problem of the basin ranges in 1901 and its melancholy sequel 

 have been told above. For a number of years thereafter Washington remained his winter 

 residence, but California became the scene of his summer labors; and there in addition to sub- 

 ordinate physiographic studies in the Sierra Nevada and to a collateral but illuminating exami- 

 nation of the earthquake of 1906, two of his greatest investigations were undertaken. It was 

 also during these later years, and wlule his attention was largely given to the work in the West, 

 that he made additions to three problems of earlier date. One concerned the rate of recession 

 of Niagara Falls and added new refinements to his earlier discussions; another explained the 



