136 The American Geologist. September, 1895 
accept the glacial theor3\ Indeed, Murchison pronounced him 
a glacialist from the reading of this address, but the adoption 
of the term "glaceo-aqueous action" for the drift showed that 
the agency of icebergs appeared the more important. There 
were three difficulties in his way: first, the immense area oc- 
cupied by the supposed ice-sheet, far greater than any known 
system of glaciers; second, the transport of boulders from 
low^er to higher levels, as from the St. Lawrence valley to the 
tops of the Green mountains and beyond ; and third the pres- 
ence of the enormous moraines near the sea coast in Massa- 
chusetts. He once remarked upon the possibility that these 
hillocks might have been the terminal moraines of this imag- 
ined ice-sheet, which is the earliest allusion to such a view 
that can be found anywhere in the annals of American geol- 
ogy- 
After returning from Switzerland he discovered in western 
Massachusetts the moraines and glacial markings of real gla- 
ciers, which he distinguished carefully from the phenomena of 
general drift supposed to have been produced by icebergs. 
Later discoveries enabled him to generalize and advocate the 
presence of glaciers upon the summits of the White and Green 
mountains and other equally high mountains by inference, 
from which bergs broke off and floated away more or less ra- 
dially. But he was careful to explain that this was a local 
glaciatlon and entirely distinct from the general drift, which 
still seemed to him to have been produced mainly by floating and 
shore ice. As his early life had been spent in a region where 
the terraces are unusually perfect, he was led naturally to 
adopt theories which would explain their origin, and thus he 
made much of the distinction between the drift and the mod- 
ified drift, asserting that the terraces had been derived from a 
re- working or assorting of the ice-made accumulations. It 
was the careful study of terraces that led to the preparation 
of the Illustrations of surface geology published by the 
Smithsonian Institution in 1857. This was, to that date, the 
most complete treatise upon surface geology that had been 
published in the LTnited States. It is to his credit that he did 
not allow himself to be led astray by any fanciful theory like 
that proposed by the brothers Rogers, who were his contem- 
