362 Transactions.—Geology. 
would at this depth have to carry would be 800 x 5000 = 4,000,000 Ibs. 
As the elasticity at the same depth is assumed to be two thousand 
times greater than at the surface, this would be equivalent to loading 
stone at the surface with a weight of 2000 lbs. per square inch, which it is 
well able to bear, especially if, as is probable, the resisting power of stone 
to compression is much increased by its increased density at the lower 
depth. There is, therefore, on this account nothing unreasonable in the 
assumption we have made, that the elasticity at a depth of 800 miles is not 
more than 2000 times greater than at the surface. Indeed, if the rocks at 
this depth are not greatly different from those we know at the surface, our 
assumption cannot be very far wrong. If the elasticity were much less 
than we have assumed it to be, the rock would be unable to bear the 
weight of the overlying strata, and would compress until sufficient heat had 
been evolved by the compression to give it the elasticity required. If on 
the other hand, the elasticity were much greater than our supposition, the 
rock would expand, lifting the weight above it until its elasticity had been 
sufficiently reduced by the loss of heat due to the expansion. 
It now remains to compare the hypothesis with the results of observa- 
tion. If it will not stand the test it must of course fall to the ground, but 
I hope to show that my deductions agree well with the records of volcanic 
action in various parts of the world. 
It would follow from what I have been endeavouring to prove, that 
lines of elevation would tend to be continuous and of considerable length. 
This is so well known to be the case that I need not take up your time — 
by giving illustrations. 
Secondly, such lines would tend to run in the cardinal points of the 
compass. A glance at the map will show that this occurs so frequently as 
to constitute a rule, although there are many exceptions—New Zealand for 
instance is a notable exception. 
The western slope of north and south mountains is generally much 
steeper than the eastern. This may, I think, be accounted for as follows: 
If a ball be conceived to be rolling along a plane surface without 
friction and to receive a blow in the opposite direction to that in which it 
is rolling, it will, if the blow be of a particular energy, be brought to rest; 
that is the motion of the ball, as well as the whole energy of the blow, has 
disappeared as energy, and has been converted into heat. 
ahs on the other hand, a blow of equal energy had been given in the 
direction in which the ball was rolling, the velocity of the ball would be 
increased, that is, the ball would derive some energy of motion from the 
blow, and only a part of the latter would be converted into heat. 
In the same way the earth masses at A, Fig. 1, receive a blow when 
