1826;] Sir James Hall on the Consolidation of the Strata, 30i 



Craigs, and in Corstorphine Hill. It is decidedly posterior to 

 the stratified class, of which it penetrates the crevices at all 

 angles, in the form of dykes or veins, like stucco cast in a 

 mould; frequently also lodging between the strata in y^s^,, 

 shapeless masses. 



As the rock in question never fails to preserve this quality of 

 universal and perfect crystallization, I heartily concur with Dr. 

 Hope in bestowing upon it the general name of Cri/siallite^ uht 

 der which are comprehended all substances of this kind, in- 

 cluding not only Whinstone and Basalt, but also Porphyry, 

 Granite, and Sienite of every description. 



The solid mass of our globe, then, in so far as it is naturally^ 

 exposed to our view, or has been penetrated by the labours of 

 the miner, would appear, (with the exception of some streams 

 which have flowed from Vesuvius, Lipari, and other volcanoes, 

 in which the rock possesses a glassy structure), to be compre- 

 hended under these two classes, Aggregates and Crystallites* 



The whole of these rocks, of both classes, furnish, at evsry 

 turn, proofs of their having undergone revolutions of the utmost 

 magnitude ; and much ingenuity has been exerted, in endea- 

 vouring to trace these changes to some consistent and rational! 

 system. But of all the active powers of nature, one only has 

 occurred to me as capable of affording a solution, in any degree 

 satisfactory of the phsenomena, — I mean the power of internal 

 heat, which, in all ages, and in various countries, has made its 

 appearance at the surface of the earth, not unfrequently from 

 under the ocean, and which still, in our own days, gives occa- 

 sional proofs of its unabated activity. 



To ascertain the reality and sufficiency of this agent, and tc^\. 

 trace the volcanic fire to its source, with tolerable probability, 

 is, doubtless, an object of great interest and curiosity ; but it 

 has always appeared to me, that the progress of geology was re- 

 tarded by a premature anxiety to enter into such investigations. 



Taking it for granted, however, as, indeed, no one can dis- 

 pute, that there frequently do arise violent exertions of heat 

 from under the bed of our ocean. Dr. Hutton held that this 

 might furnish a rational and sufficient theory of the earth, with- 

 out entering into any inquiry as to the origin of that heat ; and 

 admitting that there are many geological facts Vv'hich cannot be 

 accounted for by such a fire as that of Vesuvius, now acting at 

 the surface, in free communication with the air, he contended 

 that the case may be very different, where that same cause acts 

 at the bottom of a deep sea, and under various modifyip.^ cir- 

 cumstances, by which its operation could not fail to be influ- 

 enced. 



This, indeed, constitutes the essence of the Huttonian Theory, 

 which I learned principally in conversation with its illustrious 

 author V and which, since his death, I have taken every means 



