ELiBOtlTE-SYENITE. 1S5 



or the mineral lodes which filled-in subsequent dislocations affect- 

 ing the granite and the neighbouring rocks alike. Charpentier's 

 expression conveys most perfectly the idea which presents itself 

 to geologists who have studied these phenomena, especially in 

 granites where they are so common, whilst Carne's term, both on 

 account of its economic bearing and its scientific expressiveness, has 

 obtained a wide usage with English writers. As a means then 

 for expressing a genetic relationship between these veins and the 

 rocks which they cut, I would prefer to stick to the time-honoured 

 term "contemporaneous veins, " notwithstanding recent assumptions 

 that it is a misuse of terms and contradictory. 1 The value of a 

 term lies in the meaning it conveys, and the meaning of this term 

 is precisely the same to-day as when Carne first used it to distinguish 

 veins genetically related to the granite from those 'which are totally 

 distinct and subsequent in origin. 2 



The basic secretions, which present the appearance of in- 

 clusions in, and the contemporaneous veins, which cut through, the 

 predominating form in a great rock-mass represent opposite ex- 

 tremes of the process of differentiation in the original magma, or 

 more probably of segregation during the process of consolidation. 

 In the case of the granites the contemporaneous veins form the 



1 Trans. Roy. Irish Academy, XXX (1894), 477; Quart. Joum. Geol. Sur., 



LIU (1897), 419* 



3 Came. " On the relative ages of the veins of Cornwall." Trans. Roy. Geol. 



Soc. of Cornwall, Vol. II (1822), page 49. I am unable to say who first used the 

 term " contemporaneous veins." Dr. John Davy in 1818 (Ibid., Vol. I, pp. 

 20, 26) referred to quartz veins traversing the granite of Porth Just as belonging 

 ** to that class of veins commonly considered contemporaneous." Those which 

 were formerly called "contemporaneous veins " were in 1834 (Boase, " Primary 

 Geology," p. 355) known as veins of segregation, a term introduced by Professor 

 Sedgwick at the suggestion of Whewell "to express that they have been formed 

 by a separation of parts during the gradual passage of the mineral masses 

 into a solid state." This is the sense also in which the term " segregation " is used 

 by Professor H. Louis in the second edition of Phillips' "Ore deposits" (1896)* 

 p. 11, foot-note. 



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