190 GRANITES AND GRANITIC VEIN-STONES. [XI. 



are often coarse-grained, and include the pegmatites, tourmaline- 

 granites, and veins carrying cassiterite and columbite, frequent- 

 ly abounding in quartz. These mineral products are to be 

 regarded as emanations from the granite, and are described as 

 a granitic aura, constituting what Humboldt has called the 

 penumbra of the granite. (Bull. Soc. Geol. de France (2), IV. 

 1249. See particularly pages 1295, 1321, and 1323.) 



10. While Fournet, Durocher, and Riviere conceived the 

 granitic magma to have been purely .anhydrous, and in a state 

 of simple igneous fusion, Elie de Beaumont maintained, with 

 Poulett Scrope and Scheerer, that water had in all cases inter- 

 vened, and that a few hundredths of water might, at a low 

 red heat, have given rise to the condition of imperfect liquidity 

 which he imagined for the material of the injected granites. 

 The coarsely crystalline granitic veins were, according to him, 

 veins of injection, and he speaks of them as examples in which 

 " the phenomena essential to the formation of granite had been 

 manifested with the greatest intensity." The granitic emana- 

 tions, which are supposed to have furnished the material of 

 these veins, appear to be regarded by him as the result of a 

 process of eliquation from the congealing granitic mass. De 

 Beaumont is careful to distinguish between them and those 

 emanations which are dissolved in mineral waters, or are ex- 

 haled as volcanic vapors (page 1324). To the agency of such 

 waters he ascribes the formation of concretionary veins, which 

 are generally characterized by their symmetrically ban- Id I 

 structure. He further adds that granites, as to their mode of 

 formation, offer a character intermediate between ordinary veins 

 and volcanic and basic rocks. This is conceivable e 

 granitic veins, since these, according to him, although formed 

 by injection, and not by concretion, result from a process of 

 emanation from the parent granitic mass, which may be de- 

 scribed as a kind of segregation. 



I have thus endeavored to give, for the most part in his own 

 words, the views on the origin of granites enunciated by the 

 great French geologist in his classic essay on Volcanic and 

 Metalliferous Emanations, published in 1847. They belong to 



