AND THEIR MEETING WITH GRANITE. 89 



conceived, in consequence of the progress upwards of that 

 heat, to have possessed at any particular moment a great va- 

 riety of intermediate temperatures, between that intense pitch 

 and tlie ordinary heat of the sea. Owing to these varieties of 

 substance and of temperature, the utmost diversity of charac- 

 ter in point of tenacity, from firmness and brittleness, to the 

 most perfect phabihty and ductility, must have belonged to 

 tliC assemblage in various parts. 



Let us now suppose a rush to have taken place from below 

 upwards, of any of those bodies in a state of liquid fusion, which 

 on cooling have constituted all our unstratified substances, from 

 granite to whinstone inclusive, and that this fluid was ur- 

 ged by an irresistible force ; the consequence must be, that the 

 stratified mass would yield in various modes. Such beds as 

 were in a frangible state, would yield by the formation of rents, 

 and the others, by having their substance forced through and 

 partly dragged upwards. Into these rents and openings the un- 

 stratified piatter in fusion would enter, and would proceed up- 

 wards more or less, according to its fusibility. Whinstone, the 

 most fusible of the set, would flow the farthest, and would even 

 perhaps arrive at the surface, and there discharge itself in the 

 open air as a real lava, or, breaking through the bottom of a 

 deep sea, might constitute a submarine lava, like one of 

 those observed in Iceland by Sir George Mackenzie, 

 which, with the characteristics of a lava, have their cavities 

 studded with calcareous spar *. When I met with this ob- 



VoL. VII. M ■ servation 



* M. DE Luc, in his Elementary Treatise on Geology, p. 365. art. 3tl. has 

 undertaken to shew, that my experiments with compression are not applicable 

 to Dr Hutton's hypothesis. " When calcareous substances," (he says, p. 365.) 

 " are calcined in open air, the fised air which is produced immediately escapes, 



" and 



