Address before the Association of American Geologists. 257 



very sudden, why may not the return of the heat have been 

 equally sudden ? If so, the most powerful debacles must have 

 been the result ;* and as the ice would disappear most rapidly 

 along its southern border, perhaps in this way a current in that 

 direction may have been produced. And yet, I confess that I re- 

 gard this theory more defective in not furnishing an adequate cause 

 for the southerly course of our drift, than in any other point. 



I find another difficulty in explaining satisfactorily by this the- 

 ory, how drift could have been often carried from lower to much 

 liigher levels ; as it has been sometimes if I am not greatly 

 mistaken. Thus, the Silurian rocks of New York, and the 

 quartz rock in the valleys of western Massachusetts, have been 

 carried over, and left upon, Hoosac and Taconic mountains and 

 the Highlands of New York. It is easy to conceive how an i(ri- 

 mense sheet of ice, by its expansive power, should force portions 

 of its mass to ascend moderate declivities, of a few hundred feet, 

 but not so easy to imagine them thus forced upwards one thou- 

 sand or two thousand feet, as they undoubtedly have been in New 

 England.f 



Another difficulty results from the fact that some of the most 

 remarkable of our moraines are found, not in valleys, but on the 

 sea coast, some of them fit\y, and others one hundred miles dis- 

 tant from any mountains much higher than themselves. I refer 

 to those remarkable conical and oblong tumuh of drift, sometimes 



* A curious example illustrative of tliis point has just been communicated to 

 me by Rev. Justin Perkins, American missionary in Persia, not far from Mt. Ar- 

 arat, in a letter dated at Uoromiah, Nov. 6th, 1840. In giving an account of two 

 very powerful earthquakes experienced on and around that mountain in the sum- 

 mer of last year, he says, " The vast accumulation of snow which had been in- 

 creasing on and about the top of the mountain for so many centuries, was broken 

 into pieces, and parts of it shaken down on the sides of the mountain in such im- 

 mense quantities, that (it being midsummer, and the snow descending down as far 

 as a warm climate, and suddenly melting,) torrents of water came rolling down 

 the remainder of the mountain, and flooded the plain for some distance around its 



base." 



t In the north of Europe, also, the drift has been carried " from lower to higher 

 levels," according to Mr. Murchison ; and he imputes the stria; to " icefloes and 

 detritus, set in motion by the elevation of continental masses, and grating upon 

 the bottom of a sea." Oa the Geological Structure of jXor titer n and Central liussia, 

 &c., by Murchison and Verncuil, p. 13. London, 1841, pp. 16. Very likely the Gla- 

 cier Theorv may need some analogous modification to adapt it to this country; 

 and yet it seems to me that expanding ice is a far more powerful agent to force 

 detritus up an inclined plane, than currents of water. 



Vol. xLi, No. 2.— July-Sept. 1341. 33 



