196 RECORD OF SCIENCE FOR 188G. 



22. Poblman advances the opinion tliatin pre-glacial time a small lake 

 occupied the valley between the Niagara and Corniferons escarpments, 

 and drained northward along the line of the present Niagara gorge as 

 far as the whirlpool, and thence down the now drift-filled valley to St. 

 David's'. There appears to have been no great cataract, but three 

 small falls over the ledges of hard beds, and the stream was joined at 

 the whirlpool by a branch from the present lower channel. The chan- 

 nel of the Niagara above the Falls was apparently iu part cut by the 

 reversal of this drainage into Lake Erie by some agency of the ice age. 



These opinions lead to the conclusion that after the lakes were sepa- 

 rated at the close of the glacial period the Niagara River had only to 

 clean out the drift-filled channels of the main pre-glacial stre im to the 

 whirlpool and thence of its branch to the present outlet. Tliis explana- 

 tion of the history of the Niagara gorge would greatly- decrease the time 

 estimate, but as the amount of work accomplished by the pre-glacial 

 drainage is not known, no figures can be suggested.* 



23. Claypole discusses the drainage relations of the great lakes, and 

 shows that Chicago would be at their foot rather than head if the ele- 

 vation at Black Rock, near Buffalo, was 20-odd feet highei', so as to 

 cause the drainage of the lakes to flow through the Chicago River into 

 the Mississippi. It is thought that the channel was cut in its present 

 position owing to a glacial ice dam in the Straits of Mackinaw during 

 the retreat of the glacier, which prevented the westward tiow antl ne- 

 cessitated the excavation of the present channel.t 



24. Lalxe Lalwntan. — Russell's long-delayed monograph | on Lake La- 

 hontan has at last appeared, and the many matters of interest connected 

 with this great fossil lake are discussed in detail. The various quivs- 

 tious of sedimentation, shore phenomena, chemical deposition, etc., are 

 treated at length in their bearing on the history of the lake, the Avhole 

 forming a most important contribution to geologic science. It is only 

 possible here to give a general r6sum6 of the principal conclusions. 

 The lake filled a compound orographic basin, resulting from tlie tilting 

 of faulted blocks, and received the drainage from many thousands of 

 square miles of surrounding country, with its mechanical load and mat- 

 ter iu solution. Its history is taken up at a tune of long aridity, which 

 was followed by a period in which the water covered nearly its maxi- 

 mum area and deposited lacustrine marls and clays exceeding 150 feet 

 in thickness. It then evaporated away, with many minor oscillations, 

 and deposited vast quantities of impure carbonate of lime in a stony 

 form of tufa termed lithoid, while stream channels were carved in the 

 lacustral beds and current-bedded gravels and sands were su])erimposed 

 on the previously formed beds. Another rise of the lake followed, with 

 the dei)osition of another lacustral series, and when about half-way to 



* Am. Assoc. Proc, vol. 3n, pp. 221, 222. 



\ Ibid., pp. 222; American Naturalist, Oct., 188G, vol. 20, pp. 857, ft seq. 



|. U. S. Geological Survey, Mouograph No. 11, p. 288, plates aud map. 



