MEMOIRS OF DECEASED FELLOWS 255 



"The more general conclusion that the system of raised beaches signify 

 a succession of flexures of the earth's surface, rather than successive stages 

 of subsidence due to the gradual removal of a barrier of tide water, or the 

 gradual wear of a barrier of stone, does not rest on this single fact." 



Even then he knew something of the change of levels in the 

 Ontario basin, for he immediately says, in citing other similar facts : 

 "There is evidence that Lake Ontario, at Rochester, N. Y., has 

 stood 70 feet lower than it does now" (page 552). Some sentences 

 in the same connection illustrate his capacity for generalization. 



"While these facts abundantly prove that a simple theory of gradual drain- 

 age, by the elevation en masse of the lake regions, is entirely inadequate, 

 they are too fragmentary to define clearly the general synchronism and se- 

 quence of the local movements to which they testify. Nevertheless, it is 

 something to have learned that the writhing of the surface of the earth, 

 which has in the ages so many times remapped the continents, has also been 

 the great immediate cause of the transformations of the great lakes, and 

 that, continuing through the latest distinguishable geological epoch and its 

 prolongation the historical, it has not now ceased." 



Dr. Newberry was the first geologist to recognize the ice barrier 

 as the cause of the high-level waters in the Laurentian basin, and 

 it is interesting to find a footnote over his initials, at the bottom of 

 the same page (552), reading as follows: 



"In the discussion of these facts cited by Mr. Gilbert, and others of simi- 

 lar character, it should be remembered that the retreating glacier must have, 

 for ages, constituted an ice dam that obstructed the natural lines of drain- 

 age, and may have maintained a high surface level in the water-basin which 

 succeeded it." 



The substance of Gilbert's report in the 1873 volume of the Ohio 

 Survey had previous publication by permission in the American 

 Journal of Science in 1871. An abstract was also printed in the 

 proceedings of the New York Academy of Sciences of February 

 20, 1871 (pp. 175-178). 



In 1871 Gilbert joined the Wheeler survey of the western ter- 

 ritories and began the many years of work in the far west. From 

 1875 he was on the survey under Major Powell. The United 

 States Geological survey was organized in 1879, with Clarence King 

 as director, and young Gilbert became a member. From that time 



