Carnutuers.—Retardation of Earth's Rotation by Volcanic Action. 869 
Before concluding, I will allude to two theoriés of mountain formation 
which have been lately brought prominently before the Society—the 
“ Contraction Theory’? of the Rev. Mr. Fisher, and the ‘“ Denudation 
Theory ” as explained by Captain Hutton. 
The former explains the existence of mountains by the contraction of 
the earth’s mass, due to the radiation into space of its heat. The upper 
part of the crust does not partake of this loss of heat, and consequently 
does not contract; it becomes, therefore, too large for the space it has to 
occupy, and in some manner, not clearly explained, the excess of matter is 
supposed to be arranged into mountains. 
Captain Hutton’s theory is, that the matter brought down by denudation 
spreads over the bottom of the sea, where it attains great thickness; the 
lower parts then become warmed, in accordance with the theory that, as we 
descend into the earth, the temperature increases. Expansion takes place, 
and the superincumbent mass is lifted in a domical shape above the sea 
level. 
To both these theories there is what appears to me to be an unanswer- 
able objection. They both assume that rock will not contract when 
subjected to a compressive strain slowly applied, while we know that in 
fact it will do so to almost any extent. 
In both cases the pressure is far within the ordinary elastic limits of the 
material, and the only change that would take place would be that the 
molecules would be pressed closer together. 
Long before the pressure became excessive, the molecules would have 
time to arrange themselves in their new form, and would be prepared to 
compress still further. We should have from both theories a denser rock 
but no mountains. 
Art. LII.—On the Old Lake System of New Zealand, with some observations 
as to the formation of the Canterbury Plains, By J.°C. Crawrorp, F.G.S. 
[Read before the Wellington Philosophical Society, 29th January, 1876.] 
Havine succeeded in proving the former connection of the Islands of New 
Zealand, with its necessary sequence a great Cook Strait river, and a fresh 
water lake in the Harbour of Port Nicholson, I propose to enlarge the scope 
of the argument very considerably, for I can perceive that lakes have been 
very extensive throughout the North Island, and have played a remarkable 
part in the arrangement of the surface of the land. 
x1 
