262 COSMOS. 



made by Sir James Hall more than half a century ago, and 

 by the attentive study of granitic veins, which has contributed 

 so largely to the establishment of modern geognosy. Some- 

 times the erupted rock has not transformed the compact into 

 granular limestone to any great depth from the point of con- 

 tact. Thus, for instance, we meet with a slight transforma- 

 tion — a penumbra — as at Belfast, in Ireland, where the ba* 

 saltic veins traverse the chalk, and, as in the compact cal- 

 careous beds, which have been partially inflected by the con- 

 tact of syenitic granite, at the Bridge of Boscampo and the 

 Cascade of Conzocoli, in the Tyrol (rendered celebrated by 

 the mention made of it by Count Mazari Pcucati).* Another 

 mode of transformation occurs where all the strata of the com- 

 pact limestone have been changed into granular hmestone 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 con- 

 tact, as in the Pyrenees,^ and sometimes, as in the main land 

 of Greece, and in the insular groups in the ^Egean Sea, through 

 the intermediate layers of gneiss or mica slate. Both cases 

 presuppose a simultaneous but heterogeneous process of trans 



* Humboldt, Leitre a M. Brochant de Villiers, in the Annales dc 

 Chimie et de Physique, t. xxiii., p. 261 ; Leop. voii Buch, Geog. Brief e 

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



t On the transformation of compact into granular limestone by the 

 action of granite, in the Pyrenees at the Montagnes de Rancie, see 

 Dufrenoy, in the M^moires Gdologiques, t. ii., p. 440 ; and on similai 

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

 Mem. G6olog., t. ii., p. 379-415; on a similar effect produced by the 

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

 de Beaumont, in the G6ologie de la France, t. i., p. 72), between Tulosa 

 and St. Sebastian, see Dufrenoy, in ihe M6m. Giolog., t. ii., p. 130; and 

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

 may still be distinguished, see Von Dechen, in his G6ognosie, p. 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 pre- 

 viously existed in the form of closed rings. See Poggend., Annalen der 

 Physik, bd. xxxix., s. 105; and on the rings of aragonite deposiled 

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



X Beds of granular limestone in the granite at Port d'Oo and in the 

 Mont de Labourd. See Charpentier, Constittition Geologiqve des PyrA- 

 nies, p. 144, ] 46. 



