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 stria3 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 

 towlder 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 

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

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

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

 B °th Mr. Hall and Prof. Emmons suggest moreover, that the bottom of 

 1116 ocean would be necessarily covered with detrital matter, which 

 w °uld protect the rocky floor from the direct graving action of icebergs. 



% brother and myself entertaining very similar objections to the 

 ex planation of the phenomena by icebergs, have ventured farther, and 

 P^ceiving 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 

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

 Crust d uring an era of earthquake commotion. 



Res pecting the agencies concerned in the strewing of the detrital 

 matter, a considerable diversity of theoretical opinion prevails among 

 Vol. XLVII> No 2# _ July _ Septt 1844 . 35 



