474 Transactions.— G'eology. 
through the superficial rocks, and the waters that permeate or cover 
them, into surrounding space. Secondly, we have the phenomena of 
volcanos, proving, as has been shown, that, besides this, another consider- 
able amount of heat is continually effecting its outward escape—with less 
regularity, but with equal constancy—by the exhaustion from within of 
heated vapours and thermal waters, and the eruption of incandescent lavas. 
The continuance of these phenomena, through every past age of the globe, 
proves the accession of continual increments of caloric from great depths 
within its interior to the mass of lava, or the material from which lava is 
elaborated, that underlies the outer hardened and comparatively cool crust ;'' 
and he further remarks,—‘ That it would seem that the outward trans- 
mission of internal heat by these two combined modes is insufficient for its 
discharge as rapidly as it is supplied from within, inasmuch as a third 
collateral order of phenomena, the plutonic, attests the frequent expansion 
only to be accounted for by increased temperature of extensive underlying 
masses of matter." 
I may, moreover, in conclusion, cite the following passage from Pro- 
fessor Duncan's address, as possessing interest in connection with my 
papers. After remarking that we may readily believe in a universal 
atmosphere whose tenuity is greatest between the great attracting bodies, 
and referring to Mr. Mattieu Williams’ views on this subject, he says,— 
* Reasoning, then, by analogy, the earth should have had a higher 
atmosphere, and probably more of it in the past, and this would be very 
compensatory. A slightly greater atmospheric pressure would counteract 
the greater possible rate of evaporation; and this compensation rather 
adds to the probability of the theory. With more aqueous vapour and 
à more energetie sun, sub-aerial denudation may have progressed far above 
its present average rate. Moreover, the greater movable atmosphere 
would absorb much of the heat of the hotter sun, and would modify 
its action on the surface; and, on the other hand, a greater diffusion of — 
equable temperature would prevail, and towards the poles there would be 
prolonged twilight. A greater rainfall and more rapid movement of the 
lower zones of the atmosphere would result; and as the supply of moisture 
must have been greater, there is no reason why the local glacialization of 
high mountain ranges should not have occurred. The improbability of the 
occurrence of masses of ice on the sea-level, or for some thousands of feet above 
it or at the poles, must, however, be admitted." The italics are mine in the 
foregoing quotation, and the passages so marked bear, as will be seen, a 
good deal upon my views. 
