SIR JAMES HALL on the Consolidation of the Strata. 315 



ties in geology, that the strata, those, at least, of later forma- 

 tion, have once constituted collections of incoherent parts. And 

 it is further admitted, that these beds have undergone various 

 remarkable changes, some chemical, some mechanical. 



The chemical changes consist in the consolidation of these 

 loose assemblages into their present state of rock, passing, in that 

 transition, through boundless varieties, in point of flexibility and 

 toughness, and occasional brittleness. The mechanical revolu- 

 tions are no less remarkable, principally in the change of the 

 strata to their present contorted shape, and elevated position, of- 

 ten many thousand feet above the surface of the sea ; though there 

 is full reason to believe that they all once lay in a horizontal 

 position at its bottom. 



I have said that the greatest part of the crust of our habi- 

 table globe seems unquestionably to be stratified, and produced 

 from detritus or fragmented materials. The other portion, 

 though probably the least in bulk, is, generally, the most conspi- 

 cuous, owing to its durability, elevation, and picturesque beauty. 

 This kind of rock is contrasted with the former class, particular- 

 ly in its negative qualities ; in being, according to some geolo- 

 gists, altogether devoid of stratification in the general mass, and 

 entirely free from component fragments ; the whole being made 

 up of crystalline forms, moulded upon each other, in obedience 

 to certain chemical laws. 



This crystalline rock, as the Society are well aware, abounds 

 in the neighbourhood of Edinburgh, in Arthur's Seat, Salisbury 

 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 ; fre- 

 quently also lodging between the strata in vast shapeless masses. 



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

 universal and perfect crystallisation, I heartily concur with Dr 

 HOPE in bestowing upon it the general name of Crystallite, un- 



