Association of American Geologists and Naturalists. 269 



been ice in one vast sheet acting by mere expansion," or the same in 

 the form of stranded icebergs. Others, among whom is Prof Mather, 

 think that " there can be no doubt that the scratches on the rocks are 

 due to the movements of floating ice, containing masses of rock frozen 

 in, and grinding upon the bottom." Prof Emmons, on the contrary, 

 conceives that " the phenomena in the main are independent of the ac- 

 tion of icebergs," which he believes " to be very poorly adapted to polish, 

 groove and score rocks," and he urges that their motion when they are 

 grounded is rotatory, and therefore not such as to produce strise deviating 

 so little from a prevailing direction as those which we behold. He 

 thinks the grooved surfaces have been overflowed by wide shallow riv- 

 ers, which have smoothed and scored the rocks by pushing along grav- 

 el, sand and ice ; and confining his view to New York, he supposes 

 that these rivers communicated with the Atlantic on the south through 

 the Champlain, Hudson and Mohawk valleys, and that they bore along 

 ice loaded with sand and pebbles, which scratched and grooved the sur- 

 faces of the rocks. He thinks that the erosion occurred before the true 

 bowlder epoch. 



Mr. Hall suggests several objections to its production by angular frag- 

 ments set in the bottom of icebergs or icefloes. He mentions the di- 

 vergence of many furrows from their regular course as indicative of a 

 freedom of motion in the grooving body, and he calls attention to the 

 minuteness of the strise as implying that they were probably caused by 

 sand and gravel moved by some superincumbent even surface, " not un- 

 like the polishing of marble when the motion is all in one direction." 

 Both Mr. Hall and Prof. Emmons suggest moreover, that the bottom of 

 the ocean would be necessarily covered with detrital matter, which 

 would pi'otect the rocky floor from the direct graving action of icebergs. 



My brother and myself entertaining very similar objections to the 

 explanation of the phenomena by icebergs, have ventured farther, and 

 perceiving no necessity for supposing that the cutting fragments and 

 particles were ever pressed upon by ice, have appealed to the enor- 

 mous erosive power which a thick and ponderous sheet of angular 

 fragmentary rock would possess, if driven forward at a high velocity 

 under the waters of a deep and general inundation, excited and kept 

 in motion by an energetic upheaval and undulation of the earth's 

 crust during an era of earthquake commotion. 



Kespecting the agencies concerned in the strewing of the detrital 

 matter, a considerable diversity of theoretical opinion prevails among 



Vol. xLvn, No. 2.— July-Sept. 1844. 35 



