ON THE FORMATION OF CRYSTALLINE ROCKS. 233 



reality, the only way to do justice to the author of these fundamental 

 discoveries and to his successors. We shall follow the order adopted 

 by Hutton and his commentator. 



The author remarks in the outset that certain deposits, which he 

 qualifies as primitive, appear to have been formed in the same manner 

 as the recent sedimentary strata. It is thus that the beds of the 

 Alps, considered as primitive, cannot be anterior to the existence of 

 vegetables, since they contain numerous remains of them in the form 

 of mineral combustibles. Furthermore, other crystalline deposits con- 

 tain beds consisting of sand and pebbles; they were, therefore, formed 

 from the detritus of pre-existing deposits; for if we should admit, 

 with Deluc, that quartz sand is a chemical deposit, we cannot explain 

 why there is none existing in the midst of the most crystalline masses,. 

 particularly in granite and metalliferous veins. The compactness 

 of these rocks, which are at the same time sedimentary and crystal- 

 line in structure, could only result from the action of heat and from 

 softening. According to Hutton, if a foreign substance in a state of 

 solution had penetrated the pores of the rock, the liquid would have 

 of necessity left certain cavities. The masses of lamellar limestone 

 which often accompany this species of crystalline rock also supply 

 him with an argument; for he assumes, as beyond a doubt, that lime- 

 stone, in which Black had just discovered carbonic acid, could only 

 retain its gaseous element at a high heat when the rock was at the 

 same time submitted to great pressure. He adds that, under these 

 circumstances, carbonate of lime can even be melted. "We know that 

 this bold conjecture was afterwards confirmed by the experiments of 

 his most celebrated disciple.* 



The mod^ of occurrence of the different species of mineral com- 

 bustibles contributed to the support of this same theoretical idea. 

 After having remarked that, in the Isle of Sky, ordinary lignite 

 changes, under the basalt M'hich covers it, into a compact combusti- 

 ble, with a brilliant fracture like coal, Hutton concluded, as Buffon 

 had previously supposed, that coal had the. same origin as lignite; 

 that the beds of coal and deposits of bitumen result from the transfor- 

 mation of vegetable and mineral matter by heat and under the influ- 

 ence of pressure. 



In the generalization of this idea, he came even to include gra- 

 phite in the series of products derived from the burial and transfor- 

 mation of organic bodies. Thus, by an idea entirely new. the illus- 

 trious Scotch geologist supposed water and the internal heat of the 

 globe to have successively co-operated in the formation of the same 

 rocks. 



It is a characteristic of genius to comprise, under a common origin, 

 very dissimilar phenomena. Subterraneous heat, according to Hut- 

 ton, not only consolidated and mineralized the strata at the bottom 

 of the sea, but it had, moreover, raised and depressed beds which were^ 

 originally horizontal. Saussure had then just observed the elevation 



- Sir James Hal!, whose conclus;iun6 on the simultaneous action of heat and pressure 

 will he noticed presently. 



