Geology of America. 79 
how the long ridges of clay and gravel so common in Sweden 
and Finland, and seen also in the United States, might be 
formed, and the ideas now thrown out may serve to account 
for the north-west and south-east arrangement they generally 
affect. This arrangement would not be uniform, but would 
of course be modified by the position of mountain chains or 
high lands which rose above the water. In some cases the 
line of motion might be right southward, in others right east- 
ward, but in the greater number of cases it would be inter- 
mediate. 
If we suppose the fusion of the ice to be proceeding slowly 
for a thousand years, and numerous icebergs loaded with gravel 
and stones to be constantly detaching themselves from the 
polar nucleus, and pursuing their course south-easterly, we 
may comprehend how all the rocks at moderate depths might 
have their upper surfaces scratched and grooved in that di- 
rection. Some of the larger icebergs are believed to reach 
down 1000 feet below the surface of the water, and might 
scratch rocks even at that depth, while the smaller ones would 
operate on rocks almost close to the beach. Boulders would 
be transported by the same agency over great distances. 
Mr Murchison’s hypothesis, if adopted, does not exclude 
that of Agassiz. On the contrary, it may be assumed, that, 
while the glacical condition (which caused the great accu- 
mulation of ice in the northern regions) continued, every 
mountain chain which then had an elevation of two or three 
thousand feet above the sea, would be encrusted with ice, 
perhaps as far south as the latitude of 40. Each of these 
would be on a small, what the polar nucleus of ice was ona 
great scale—a “ centre of dispersion.” Grooving clearly re- 
ferrible to glacial action, has been traced on Jura and the 
Vosges, and I believe also on the Scandinavian chain as well 
as the Alps. 
Mr Lyell has shewn that in the present state of our know- 
ledge, the distribution of erratic blocks cannot be explained, 
without assuming the agency of floating masses of ice in trans- 
porting some of them. We have a good example at hand in 
the Pentland Hills, where a block of mica-slate, which must 
have travelled from the Grampians, may be seen resting on 
