T. S. Hunt on Granitic Bocks. 87 



He further adds that granites, as to their mode of formation, 

 offer a character intermediate between ordinary veins and vol- 

 canic and basic rocks. This is conceivable as regards granitic 

 veins, since these, according to him, although formed by injec- 

 tion, and not by concretion, result from a process of emanation 

 from the parent granixic mass, which may be described 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, pubhshed m 1847. They be- 

 long to the history of our subject, and are remarkable as a 

 clear and complete expression of those modified plutonic views 

 which are probably held by a great number of enlightened 

 geologists at the present time. My reason for dissenting from 

 them, and the theories which I offer in their stead will be shown 

 in the sequel. 



§ 11. Elie de Beaumont, while regarding the formation of 

 granitic veins as a process in which water intervened to give 

 fluidity to the magma, was careful to distinguish the process 

 from that of the production of concretionary veins from aqueous 

 solution, and supposed the fissures to have been filled by the 

 injection of a jet of pasty matter, derived from a consolidating 

 granitic mass. Daubree and Scheerer in describing the granitic 

 veins of Scandinavia, conceive the material filling them to have 

 been derived from the enclosing crystalhne strata instead of an 

 unstratified granitic nucleus, but do not, so far as I am aware, 

 compare their formation to that of concretionary veins. Their 

 publications on this subject, it should be said, are both anterior 

 to the essay of de Beaumont 



§ 12. The notion that all granitic veins are the result ot 

 soQie process of injection, and not to be confounded with con- 

 cretionary veins, seems indeed to have been general up to the 

 present tune. Even von Cotta, while strongly maintaming 

 the aqueous and concretionary origin of metalliierous vems m 

 general, when describing those consisting of qaartz, mica, 

 feldspar, tourmaline, garnet and apatite, with cassitente, wol- 

 fram, etc., which occur at Zinnwald and at Johanngeorgenstadt, 

 is at a loss whether to regard these veins, from their granitic 

 character, as igneous-fluid injections or as concretionary lodes. 

 In support of the latter view he refers to their more or less 

 regular and symmetrically banded structure, and whfle recall- 

 ing the fact that mica and feldspar may both be foimed m the 

 humid way, considers the nature of these veins to be very prob- 

 lematical, and the question of their origin a difficult one.— (Oe 

 Deposits, Prime's translation, 1870, pages 110-124). 



§13. I have for several years taught that granitic veins ot 

 the kind just referred to are concretionary and of aqueous ongm. 



