267 



fissures filltd with rock-salt, which occurred in such consider- 

 able masses, as occasionally to lead to its being disposed of 

 by contraband trade. On both declivities of the Pyrenees, 

 the connection of diorite and pyroxene, and dolomite, gyp- 

 sum and rock-salt cannot be questioned;* and here, as in the 

 other phenomena which we have been considering, everything 

 bears evidence of the action of subterranean forces on the 

 sedimentary strata of the ancient sea. 



There is much difficulty in explaing the origin of the beds 

 of pure quartz, which occur in such large quantities in South 

 America, and impart so peculiar a character to the chain of 

 the Andes. f In descending towards the South Sea, from 

 Caxamarca towards Guangamarca, I have observed vast 

 masses of quartz, from 7000 to 8000 feet in height, superposed 

 sometimes on porphyry devoid of quartz, and sometimes on 

 diorite. Can these beds have been transformed from sand- 

 stone, as Elie de Beaumont conjectures in the case of the 

 quartz strata on the Col de la Poissonniere, east of Briangon?! 

 In the Brazils, in the diamond district of Minas Geraes and 

 St. Paul, which has recently been so accurately investigated 

 by Clausen, plutonic action has developed in dioritic veins, 

 sometimes ordinary mica, and sometimes specular iron in 

 quartzose itacolumite. The diamonds of Grammagoa are 

 imbedded in strata of solid silica, and are occasionally 

 enveloped in lamina? of mica, like the garnets found in mica 

 slate. The diamonds that occur furthest to the north, as 

 those discovered in 1829 at 58 lat., on the European slope 

 of the Uralian Mountains, bear a geognostic relation to the 

 black carboniferous dolomite of Adolffskoi and to augitic 

 porphyry, although more accurate observations are required 

 in order fully to elucidate this subject. 



Amongst the most remarkable phenomena of contact, we 

 must, finally, enumerate the formation of garnets in argil- 

 laceous schist in contact with basalt and dolerite, (as in 

 Northumberland and the Island of Anglesea), and the occur- 



* Dufrenoy, in the Memoires geologiques, t. ii. p. 145 and 179. 



t Humboldt, Basal geogn. sur le Gisement des Roches, p. 93- As\ 

 ctntrale, t. iii. p. 532. 



t Elie de Beaumont, in the Annales des Sciences N&turelles, i. X7. 

 p. 3o2 ; Murchison, Silurian System, p. 286. 



B.06C, Relse nock dew. Ural, bd. L a. 364 und 367. 



