650 



GEOLOGY. 





granite ; but in Charnwood Forest, in our own country, beds belonging to the same 



series lie horizontally upon 

 the abrupted granite, here 

 shown. It follows that the 

 granite of Charnwood was 

 elevated before the deposi 

 tion of the strata, and the 

 granite of the Alps subse 

 quent to it ; and as simi- 



Granite of Charnwood. lar Ca l care0 us formations, 



containing similar organic remains, must be regarded as of contemporaneous origin, we 

 are here presented with an instance of granites of different ages, the English older than 

 the Alpine. Nothing can be more conclusive upon this point than the circumstance 

 of granitic veins traversing granite, an example of which is given, from the vicinity 



of Carlsbad in Germany, decisively 

 proclaiming the two eras of the 

 formation of the mass. In the Pyre 

 nees, according to M. Dufrenoy, gra 

 nite veins occur in limestones refer 

 able to the upper secondary strata ; 

 at Weinbohla in Saxony, and in the 

 county of Antrim in Ireland, the 

 chalk belonging to the same series 

 is overlaid by the granite, which 

 shows its production at the epoch of 

 the chalk ; and M. Von Buch, De 

 Beaumont, and De Luc refer the 

 elevation of the granite of the western 

 Alps, extending from the Mediter 

 ranean to Mont Blanc, to the still 

 Granitic Veins in Granite. more recent tertiary era, and the 



eastern range is supposed not to have been upreared until after the deposition of all the 

 tertiary strata. Mr. Darwin, also, has advanced the opinion that the granite of the South 

 American Cordilleras is of the same comparatively modern date, and has entered and 

 contorted beds belonging to the tertiary series. 



There are several igneous rocks, which, though not mineralogically granitic, are 

 commonly classed with the granite group, as primitive porphyry, whose base is felspar ; 

 diallage-rock, a compound of diallage and felspar ; and serpentine, which forms large 

 masses in its simple mineral state, but is more frequently combined with diallage. 



Diallage the saussurite of some French writers, from its being first noticed by Saus- 

 sure scattered in loose blocks over a valley near the Lake of Geneva, and the gabbro of 

 Von Buch is generally of a greenish colour, and sometimes so unconquerably hard as 

 to defy all attempts to remove it by blasting. It occurs in the valley of Saas in the 

 Haut Valois, enormous blocks being brought down by the glaciers which descend from 

 Mont Rosa. It is found there also in beds, and on the Italian side of the Alps, in the 

 Apennines, in Norway, at the North Cape, and in other districts. Diallage was known 

 to artists long before it attracted the attention of geologists. The Grand Duke Ferdinand 

 de Medicis caused numerous blocks of it to be transported from Corsica to Florence in 

 1604, where, under various forms, it ornaments the Laurentine chapel. On account of its 

 great hardness and peculiar tenacity, it is used in Vienna as the ordinary paving-stone. 



