502 Geological Society. 
examined them in great detail, and left few of their phenomena 
uninvestigated. Hugi also, in his account of the Alps, and Scoresby, 
in his descriptions of the arctic regions, have communicated much 
valuable information respecting glaciers, but without giving rise 
to any important geological results; and it was Venetz and De 
Charpentier who first ascribed to them the transport of the erratic 
boulders of Switzerland, supposing that the Alps formerly attained 
a greater altitude than at present, and that the glaciers extended to 
the plains of Switzerland, and even to the Jura. This assumed 
greater height of the Alps M. Agassiz dissents from, as no geolo- 
gical phenomena compel him to admit it; and the arrangement of 
the boulders proves that the blocks were not pushed forward by the 
glaciers, as conjectured by M. Charpentier. Moreover, the phe- 
nomena of erratic boulders extend over all the temperate and north- 
ern regions of Europe, Asia and America, and, consequently, could 
not depend upon so local an event as a greater altitude of the Alps. 
The consideration of these difficulties induced M. Agassiz to resume 
the study of glaciers; and after devoting the suitable portion of five 
successive summers to the study of their details, and all that has 
been written respecting their structure, he has arrived at the con- 
viction, that the formation of glaciers did not only depend upon the 
actual configuration of the earth, but was also connected with the 
last great geological changes in the surface of the globe, and with 
the extension of the great mammifers still found in the polar ice. 
He has also convinced himself the glaciers did not advance from the 
Alps into the plains, but gradually withdrew towards the mountains 
from the plains which they once covered. In this belief, he says, 
he is supported by many considerations which escaped previous ob- 
servers, depending chiefly on the form and relative position of the 
erratic blocks, and the commonly called diluvial gravel, the former 
being in Switzerland always angular, and resting on the latter, 
which consists of rounded materials. Considered in this point of 
view, glaciers assume an entirely new importance, for they introduce 
a long period of intense cold between the present epoch and that 
during which the animals existed, whose remains are buried in the 
usually called diluvial detritus. 
Having established his theory as completely as he could, by re- 
peated investigations of Switzerland and the adjacent portions of 
France and Germany, M. Agassiz became desirous of examining a 
country in which glaciers no longer exist, but in which traces of 
them might be found. This opportunity he has recently enjoyed, 
by examining a considerable part of Scotland, the north of England, 
and the north, centre, west and south-west of Ireland; and he has 
arrived at the conclusion, that great masses of ice, and subsequently 
glaciers, existed in these portions of the United Kingdom at a period 
immediately preceding the present condition of the globe, founding 
his belief upon the characters of the superficial gravels and erratic 
blocks, and on the polished and striated appearance of the rocks in 
situ. 
M. Agassiz does not suppose that his views respecting glaciers 
