September 3, 1886.] 



SCIENCE. 



205 



PROCEEDINGS OF THE GEOLOGICAL 

 SECTION. 



The geological interest of the meeting at Buffalo 

 naturally centred in the excursion to and discus- 

 sion of the falls and gorge of Niagara. Dr. Pohl- 

 man of Buffalo described the district to be visited 

 on Saturday, and called particular attention to the 

 occurrence of drift-filled antecedent channels on 

 the line selected by the post-glacial overflow of 

 Lake Erie, which u^ould greatly diminish the 

 amount of rock-cutting required in the excava- 

 tion of the present gorge, and thus reduce the 

 time since the overflow began : indeed, he thought, 

 that, while there may have been rapids in the 

 course of the early Niagara, near the Lewiston 

 margin of the limestone plateau, in which the 

 gorge is cut, the limestone was there so thin, and 

 the shales below it so weak, and branching ante- 

 cedent channels guided so great a length of the 

 gorge from the plateau margin towards the pres- 

 ent falls, that no great cataract was formed until 

 the gorge was cleaned out even as far up as the 

 older suspension-bridge. This would leave but a 

 small amount of deep, hard rock-cutting for the 

 falls to accomplish, and would thus make their 

 beginning much more recent than has generally 

 been supposed. 



The geological members of the excursion party 

 therefore gave close attention to these matters, 

 and, as a whole, regarded the heavy drift between 

 the sloping, rocky banks at the whirlpool, and the 

 wide, open valley, with its plentiful drift, at St. 

 David's, as sufficient evidence of an old buried 

 channel connecting these points, and probably head- 

 ing up above the whirlpool towards the bridges. 

 But there seemed no sufiicient reason for any con- 

 fident belief in a branching old valley from the 

 whirpool towards the Lewiston bluffs : in making 

 this lower part of the gorge there must have been 

 a long period of deep rock-cutting between the first 

 leap of the falls over the bluff and the time of 

 their discovering the old drift channel at the whirl- 

 pool. It should be noted that Professor Claypole 

 reported the finding of a ledge of limestone, not 

 seen by the rest of the party, in the drift slope at 

 the whirlpool, w^hich would suggest a less depth 

 for the old valley than was generally accepted. 

 Some antecedent channelling of the rocks was, 

 however, certainly accomplished before the Niagara 

 began its flow, and the washing-out of the drift 

 that filled the old channel was easy work for the 

 river ; but by far the greater part of the gorge 

 still seems to be the original work of the falls in 

 solid rock. 



The estimate of the age of the falls was presented 

 by Messrs. Woodward and Gilbert of the geological 



survey, and their remarks greatly interested a 

 large audience that had gathered on the announce- 

 ment of the discussion. Mr. Woodward had just 

 completed a survey of the Horseshoe Falls, and by 

 comparing his results with those of the state survey 

 in 1842, and of the lake survey in 1875, he found an 

 average recession for the whole face of the fall of 

 about two and four-tenths feet per annum ; but, 

 as the central parts of the curve where the water 

 is deepest has retreated from two hundred to two 

 hundred and seventy-five feet in the eleven years 

 since 1875, an average retreat of five feet per 

 annum does not seem at all improbable. Mr. 

 Gilbert then discussed the beginning of the falls 

 as controlled by the drainage of the lakes. When 

 the retreating ice-sheet stood so as to obstruct the 

 St. Lawrence and Mohawk drainage channels to 

 the east, a broad sheet of water, representing a 

 confluent of Erie and Ontario, stood at a high 

 level over the present Niagara limestone plateau, 

 and probably drained south-westward to the Ohio. 

 When further melting opened the Mohawk Chan- 

 nel, the great double lake fell to a lower level, 

 and was separated into its two members, Ontario 

 sinking to the level of its outlet at Rome in central 

 New York, but Erie being held higher by the rim 

 of the Niagara plateau. This was the birth of the 

 river and the falls, and since then they have been 

 at work on the gorge. The age of the falls thus 

 carries us back to a tolerably definite point in the 

 decline of the glacial period. 



On the supposition of a uniform rate of reces- 

 sion, the age of the falls equals the length of the 

 gorge divided by the annual recession ; but the 

 rate has been undoubtedly varied by changes 

 in a variety of conditions, which must be allowed 

 for. As thus qualified, Mr. Gilbert gave it as his 

 conclusion that the maximum length of time 

 since the birth of the falls by the separation of the 

 lakes is only seven thousand years, and that even 

 this small measure may need significant reduc- 

 tion. 



Mr. A. A. Julien, in a paper on ' Methods of 

 testing building-stones for absorption, freezing, and 

 fire,' gave what he considered the proper condi- 

 tions for such testing, and maintained that the 

 tested stone should be continued under pressure 

 at least a month. He stated that frost was found 

 to be more active in removing particles that had 

 been loosened by chemical weathering than in 

 direct mechanical breaking of unweathered rock. 

 Mr. J. C. Branner reported that he had found 

 glacial striations over the summits of some moun- 

 tains examined by the Pennsylvania geological 

 survey, so that no direct measure of the maximum 

 thickness of the ice can be determined from this 

 region. It is interesting to note in this connection 



