196 RECORD OF .SClENCr: FOR 1886. 



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

 occupied the valley between the Niagara and Coruifeious escarpments, 

 aud 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 huve been no great cataract, but three 

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

 the whirli)ool by a branch from the present lower channel. The chan- 

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

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



These 0[)inious lead to the conclusion that after the lakes were sepa- 

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

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

 whirlpool and thence of its branch to the present outlet. This 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 llock, near Buffalo, was 20-odd feet higher, so as to 

 cause the drainage of the lakes to flow through the Chicago liiver 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 <luring 

 the retreat of the glacier, which prevented the westward flow and ne- 

 cessitated the excavation of the present channel. t 



24. Lal-e Lahontan. — Russell's long-delayed monograph | on Lake La- 

 hontau has at last appeared, aud the many matters of interest connected 

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

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

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

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

 possible here to give a general resum^ of the principal conclusions. 

 The lake filled a com])Ound orographic basin, resulting from the tilting 

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

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

 ter in solution. Its history is taken up at a time of long aridity, which 

 was ibllowed 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, 

 aud dei)osited vast quantities of impure carbouate of lime in a stony 

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

 lacustral beds aud current-bedded gravels and sands were superimposed 

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

 the deposition of another lacustral series, and when about half-way to 



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



\Ibid., pp. 222; American Naturalist, Oct., 188G, vol. 20, pp. 857, et acq. 



t U. S. Geological Survey, Monograph No. 11, p. 288, plates and map. 



