248 Address before the Association of American Geologists. 



cially in Switzerland. It appears too, that those countries abound 

 in those peculiar accumulations of gravel and bowlders to which 

 I have referred, and which are now regarded as ancient moraines. 

 Bowlders, also, appear to have been dispersed in a similar manner 

 on both continents. 



If I do not greatly mistake, the drift of this country exhibits 

 usually the following lithological characters and superposition. 

 The principal mass of the drift consists of coarse sand, pebbles, 

 and bowlders, often several feet in diameter, usually mixed to- 

 gether confusedly, but sometimes exhibiting, at least for small 

 distances, more or less of a stratified arrangement. This mass of 

 detritus, not unfrequently one hundred feet thick, occupies the 

 lowest position ; that is, it rests immediately on the smoothed and 

 striated rocks in place. Sometimes there is mixed with it fine 

 sand or mud ; and occasionally a limited mass of clay, appearing 

 as if out of its original position. Above this deposit, in most of 

 the larger valleys, as those of the Hudson, Connecticut, and Pe- 

 nobscot, and in many smaller ones, we find horizontal layers of 

 fine blue clay, rarely as much as one hundred feet thick. Above 

 the clay, and of less thickness, we have a bed of sand, becoming 

 coarser towards the top, and exhibiting sometimes at its surface, 

 marks of a stronger movement in the waters by which it was de- 

 posited, than could have taken place while the clay was in a 

 course of formation. Scattered over the whole surface, but con- 

 fined chiefly to the region abounding in gravel, we find insulated 

 blocks, sometimes rounded and sometimes angular. 



Now if I have not mistaken the recent descriptions of Euro- 

 pean drift, its composition and arrangement correspond with those 

 of the drift of this country ; and scarcely any thing seems want- 

 ing to make out a complete identity. 



It is well known that the theory of drift has for some years 

 been the most unsettled part of geology. The mass of geolo- 

 gists have, indeed, admitted that in some way or other, currents 

 of water have been the principal agency employed, because they 

 witness somewhat analogous effects from aqueous action ; and, 

 until recently, no other power of adequate energy and extent has 

 been known to exist. Hence they have been willing to retain 

 the term diluvial, as a generic expression, implying simply aque- 

 ous agency in general. Yet so many difficulties attend any the- 

 ory of mere currents, that many geologists have become sceptical 



