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to say that at some depth or other we should expect to find 
mineral matter in a state of fusion; that is in the condition 
called lava. Now we know the effect of water coming in con- 
tact with ignited or red-hot substances; the result is a series of 
explosions. If we watch molten iron issuing from a furnace 
the fused mass is not explosive, but pour water upon it, and 
explosions follow. Suppose now that these explosions, due to 
pouring water on molten mineral matter, were to take place in a 
confined space, then there would be a violent effort of the steam 
and water vapour to escape. The enclosing surface would be 
subject to violent. shocks and pressure, and at last, probably, 
the force of the steam would overcome the strength of the 
enclosing surface and it would yield at some weak point. I 
think this is something similar to what takes place in the case 
of volcanic eruptions. But the question comes’ how can the 
water get to the depths of fusion? That the strata of the 
earth holds immense stores of water is well known, but 
whether it would be possible for it to percolate to the depths 
of fusion is a question for consideration. The difficulty is not 
so much in the mechanical percolation, but in the fact that as the 
liquid approached the lava it would be converted into steam, and 
probably water vapour, which would act as an elastic cushion, 
as it were, between the pressure of the descending water and 
the lava. I think the evidence is against the proposition of 
water finding access to the depths of fusion by percolation 
through the strata, but there are other ways by which such a 
result might be practicable, which I will now consider. 
* That the earth is undergoing a gradual cooling process is 
generally accepted. By that cooling the crust of the earth 
has undergone a certain amount of contraction and shrinkage, 
and the process is probably going on still. As a result strata 
has been faulted, and elevations and depressions have occurred 
all over the surface. Mr Mallet tried to account for the heated 
conditions of rocks at great depths as due to the friction and 
pressure produced by the crushing process resulting from the 
shrinkage. Though I am not prepared to accept that theory. 
I look upon the contraction of the crust of the earth as possibly 
