474 Transactions. — Geology. 



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 heen 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 fm-ther 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 

 pajDers. After remarking that we may readily beheve 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, — 

 " Eeasoning, then, by analogy, the earth should have had a higher 

 atmosphere, and probably more of it in the past, and this would be very 

 comx^ensatory. 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 

 a more energetic 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 toivards 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 tjie 

 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. 



