The Glacial Theory of Prof. Agassiz. 365 
vennes are probably a third; and the Pyrenees a fourth. We have 
one of vast magnitude in the Scandinavian mountains, whose travelled 
blocks are found scattered over northern Europe, from the shores of 
England to Moscow. In this country Agassiz considers the Grampians, 
_ the Cumberland mountains, and those of Wales, as centres of dispersion. 
There is a question arising out the theory, which he has not touched 
upon. If we suppose the region from the 35th parallel to the north 
pole to be invested with a coat of ice thick enough to reach the sum- 
mits of Jura, that is, about 5000 French feet, or one English mile in 
height, it is evident that the abstraction of such a quantity of water 
from the ocean would materially affect its depth. The area of the 
Space extending 55 degrees on each side of the pole, is pretty correctly 
two-sevenths of the whole surface of the globe. Supposing two-thirds 
of this space to be dry land, and the spongy coat of ice equal to two- 
thirds of its bulk of water, and assuming, what is pretty near the truth, 
that the sea occupies three-fourths of the surface of the globe, we find 
that the abstraction of the water necessary to form the said coat of ice, 
would depress the ocean about 800 feet. Admitting further, that one- 
eighth of the fluid yet remains locked up in the existing polar ices, it 
follows that the dissolution of the portion which has disappeared would 
raise the ocean nearly 700 feet. ‘The only very ‘Uncertain element 
here is the depth of the ice; but even if this should be reduced ‘one- 
half, we would still have an agent capable of producing a change of 
350 feet on the level of the sea. We are besides leaving out of view 
the southern polar region, which it is now known embraces a great 
extent of land. If this was also covered with ice, the change would 
be much greater than we have assumed. 
These very original and ingenious speculations of Professor Agassiz 
must be held for the present to be under trial. They have been deduced 
from a limited number of facts observed by himself and others, and 
skilfully generalized ; but they cannot be considered as fully estab- 
lished till they have been brought to the test of observation in distant 
parts of the world, and under a great variety of circumstances. Suppo- 
sing the theory to be substantially sound, the magnitude of the conse- 
quenees it involves will undoubtedly bring objections to light, which may 
render modifications necessary, both in its principles and its details. 
In the mean time, it assists us in resolving some difficulties. [t contri- 
butes, in a greater or less extent, to explain the dispersion of erratic 
. blocks, the dizarre situations they occasionally occupy, the banks of 
clay and gravel found on the sides and at the mouths of valleys, the 
. striae, polishing and grooving, observed on the surface of rocks im siti, 
and of large stones in the till; and it promises to throw light on what 
is at present a very obscure subject, the origin of the older and newer 
alluvium. 
