GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 213 



are justified in saying, as a general fact, that during their deposi- 

 tion, organic beings could hardly have existed in the vicinity. 

 And yet some hundreds of years, it would seem, must have been 

 occupied in their deposition. 



Before proceeding to the theoretical part of this subject, it 

 would be desirable to answ^er the inquiry, how far south in our 

 country the phenomena that have been described are to be found ? 

 And from aU the information within my reach, I incline to the 

 opinion that scarcely any trace of drift, or stria?, exists in our 

 Southern States. As yet we have no facts of any consequence 

 stated by geologists, south of Virginia, on this subject. I know 

 not what facts may be in the note-books of our southern geolo- 

 gists ; but should not think it strange, if beyond the State just 

 mentioned, no vestiges of glacio-aqueous action should be found, 

 except perhaps upon the high mountains. And yet De la Beche 

 states from personal observation, that Jamaica, in the West Indies, 

 does contain erratic blocks, scattered by this agency : and the 

 late Professor Hovey, who spent two winters in those islands, 

 confirms this statement. We should not then be yet too sure 

 how far south these phenomena extend. Professor H. D. Rogers 

 informs me that primary pebbles do occm" in Tennessee. 



Theories of Drift. 



Having occupied so long a time in describing the phenomena 

 of drift, I must be brief in discussing the theories of its origin. 

 And yet those theories have of late assumed a very interesting 

 aspect. 



If I am not much mistaken, geologists of every school, with 

 perhaps a few exceptions, would now assent to the general pro- 

 position, that the phenomena of drift have been the result of the 

 joint action of ice and water. They would differ as to the share 

 which each of these agents has had in the work, while they 

 would agree that both must have been more or less concerned. 

 As I understand the subject, the principal diversity of opinion 

 that now exists, relates to the mode in which these agents have 



