at 
248 Address before the Association of American Geologisis. ~ 
cially in Switzerland. It appears too, that those countries abound 
in those peculiar accumulations of gravel and bowlders to which 
[ 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 
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. ad 
Now if Ihave 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 wapt- 
ing to make out a complete identity. — si 
It is well known that the theory of drift has for some yeas 
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 
Pape 
ous ageficy in general. Yet so many difficulties attend-any the 
