. 



HOCKS. 263 



largely to the establishment ot modern geognosy. Sometimes 

 the erupted rock has not transformed the compact into granular 

 limestone to any great depth from the point of contact. Thus, 

 for instance, we meet with a slight transformation a penum- 

 bra as at Belfast in Ireland, where the basaltic veins traverse 

 the chalk ; and, as in the compact calcareous beds, which have 

 been partially inflected by the contact of syenitic granite, at 

 the Bridge of Boscampo and the Cascade of Canzocoli, in the 

 Tyrol, (rendered celebrated by the mention made of it by 

 Count Mazari Peucati.)* Another mode of transformation 

 occurs where all the strata of the compact limestone have 

 been changed into granular limestone by the action of granite, 

 and syenitic or dioritic porphyry.f 



I would here wish to make special mention of Parian and 

 Carrara marbles, which have acquired such celebrity from the 

 noble works of art into which they have been converted, and 

 which have too long been considered in our geognostic collec- 

 tions as the main types of primitive limestone. The action of 

 granite has been manifested sometimes by immediate contact, 

 as in the Pyrenees,! and sometimes, as in the mainland of 

 Greece, and in the insular groups in the ^Egean sea, through 



* Humboldt, Lettre d M. Brochant de Villiers, in the Annales de 

 Chimie et de Physique, t. xxiii. p. 261 ; Leop. von Buch, Geog. Brief* 

 iiber das sudliche Tyrol, s. 101, 105, und 273. 



f On the transformation of compact into granular limestone, by the 

 action of granite, in the Pyrenees at the Montagues de Rancie. see 

 Dufrenoy, in the Memoires geologiques, t. ii. p. 440 ; and on similar 

 changes in the Montagues de VOisans, see Elie de Beaumont, in the 

 Mem. geolog., t. ii. pp. 379-415; on a similar effect produced by the 

 action of dioritic and pyroxenic porphyry (the ophite described by Elie 

 de Beaumont, in the Geologie de la France, t. i. p. 72), between Tolosa 

 and St. Sebastian, see Dufrenoy, in the Mem. geolog., t. ii. p. 130 ; and 

 by syenite in the Isle of Skye, where the fossils in the altered limestone 

 may still be distinguished, see von Dechen, in his Geognosie, s. 573. 

 In the transformation of chalk, by contact with basalt, the transposition 

 of the most minute particles in the processes of crystallization and 

 granulation, is the more remarkable, because the excellent microscopic 

 investigations of Ehrenberg have shown that the particles of chalk 

 previously existed in the form of closed rings. See Poggend. Annalen 

 dcr Physik, bd. xxxix. a 105 ; and on the rings of aragonite deposited 

 from solution, see Gustav Rose, in vol. xlii. p. 354 of the same journal. 



J Beds of granular limestone in the granite at Port d'Oo, and in th 

 Mont de Labourd. See Charpentier, Constitution giologique dts Pyr& 

 &*, pp. 144, 146. 



