504 PROCEEDINGS < >F COLUMBUS MEETING. 



the argument that the subsidence advances in proportion to the load imposed is 

 untenable, because, whatever the amount of depression may be, the cavity will be 

 filled if sediment be sufficiently abundant and cannot be more than tilled under 

 any conditions. In many known cases also subsidence has ceased jnst when the 

 load was greatest, the cavity being full. 



Professor Emerson said: 



The communication bears on the question as to whether the Pleistocene sub- 

 mergence of many northern lands was due to the weight of ice-sheets laid down 

 over these lands, and would seem to give an affirmative answer, except that it fails 

 to explain why the sinking lag^-d -,, long behind the loading. 



Mr. McGee rejoined : 



A principal purpose of the paper is to define the limitations of isostatic action 

 and to show that this cause is incompetent to produce the grander features of the 

 earth's surface exemplified by the Rocky mountains, the Gulf of Mexico and other 

 continents and seas — i. e., features due to the movement- classed as antecedent, — 



yet that it is competent to produce such minor warping of the terrestrial crust as 

 that displayed by the present shores of the Gulf of Mexico and by ancient forma- 

 tions in many part- of the world. The fact of subsidence at a rate proportioned to 

 the length and activity of the tributary rivers in every important deposition tract 

 of the globe cannot be gainsaid, and to me it is absurd to hold that the length of 

 the Mississippi or the Amazon or the Indus is determined by the rate at which its 

 delta is sinking. The Netherland and New Jersey coasts are indeed subsiding 

 rapidly : yet it is to be remembered that by reason of geographic conditions, includ- 

 ing not only the configuration of coasts but the action of tides and currents, sedi- 

 mentation is in both eases confined to areas far smaller than those of degradation. 

 The theory of isostacy indeed makes for the doctrine of the persistency of rivers 

 and even of continents and oceans, but no more strongly than the facts of geology. 

 Rivers are the most persistent features of the earth, and the tendency of recent 

 research is to indicate the long, though not endless, persistence of the grander geo- 

 graphic features. 



The second paper of the day was on — 



PRE-GLACIAL DRAINAGE OF SUMMIT COUNTY, OHIO. 

 BY E. W. CLAYPOLE. 



Remark- wereoffered by W. H. Sherzer, ( r. F. Wright and <i. K. Gilbert. 



The following papers were next read : 



OBSERVATIONS RELATING TO THE FORMATION OF LAKE GENEVA, 



SWITZERLAND. 



BY G. FREDERICK WRIGHT. 



The paper was illustrated by charts and diagrams. 



