1870.] 63 [Perry. 



the location of perched rocks, they being often found in extraordi- 

 nary abundance on isolated summits ; and the position of certain 

 old beaches, as that of the shore-remains at Ripton, Vermont.^ 



These, and other kindred facts, having been advanced as decisive 

 proof of glacial agency, Mr. Perry proceeded to enquire, under what 

 form, according to the evidence, the ice must have acted? Were the 

 phenomena in question produced by icebergs, as supposed by Sir 

 Charles Lyell and the geologists of his school, in connection with a 

 general depression of the country? The several cited effects of gla- 

 cial agency having been passed in review and subjected to close 

 scrutiny, it was found that the larger proportion of them could never 

 have been produced by icebergs ; that the remainder may be better 

 explained in another way ; that for the most part the theory of 

 depression is entirely unsupported by facts, and therefore to be 

 discarded. 



The iceberg hypothesis having been considered, Mr. Perry next in- 

 quired whether the results were produced in connection with a gen- 

 eral elevation of the country, at the close of the Tertiary Era, as held 

 by Professor Dana. It was shown that the theory of elevation is also a 

 mere supposition, wholly unauthorized by positive evidence ; that the 

 facts relied on for its support, as change of climate, the existence of 

 pot-holes, of fiords, and of aerial deposits now lying beneath the level 

 of the sea, can all be more satisfactorily explained in the light of an- 

 other view ; and that instead of an elevation of the land there was 

 perhaps far more probably a depression of the ocean. 



Having discussed the inadequacy of the theory of elevation, Mr. 

 Perry finally noticed the theory of glaciation substantially as proposed 

 and defended by Professor Agassiz. He inquired whether all the 

 main facts passed in review be not just what we must suppose they 

 would have been in case the country had been covered by an im- 

 mense sheet of ice moving slowly southward. In the light of this 

 view, he indicated how the several classes of effects indicative of ice- 

 agency receive a simple and easy explanation, and especially that the 

 more difficult phenomena, as perched rocks, elevated pot-holes, the 

 Bipton Beach, tlie Berkshire boulder trains, and other kindred points, 

 are not anomalies, but special instances and illustrations of the work- 

 ing of the great agency characteristic of the glacial times. 



