L. A. Necker de Saussure Voyage en Ecosse. 187 



tallization of the vein-granite has been influenced by the 

 greater or less width of the fissures ; wherever these were too 

 narrow to permit the entire developement of the crystallization, 

 the crystals have remained small and confused ; which has not 

 happened in the larger veins, where the grain of the granite is 

 coarser, and the crystals of feldspar and quartz greater and 

 more regular. 2d. We find dispersed through the granite of 

 the veins and that adjoining their junction, small fragments of 

 slate ; sometimes even considerable slaty masses completely 

 buried and enveloped in the granite. 



The partisans of the system of Werner for a long time refused 

 to admit the existence of similar veins, issuing from a mass of 

 granite, to enter into rocks, which appeared newer in their 

 eyes. They accused those of careless observation, or of being 

 misled by imagination, who first announced these facts incom- 

 patible with the theory of their master. Obliged finally to 

 yield to the force of truth, they have contrived several expla- 

 nations to reconcile these phenomena with the Werneriaa 

 theory ; and, have often, says Mr. Necker, made the evi- 

 dence of facts give way to the desire of supporting an hypo- 

 thesis. It has been said, 1st. that these pretended veins of 

 granite could be nothing but the continuation of the veins 

 of granite, which, after having traversed the mass of 

 the large-grained granite, had penetrated into the schist ; 

 and, that it was consequently a granite of a more recent for- 

 mation than that of the mountain mass, or of the schist itself; 

 a formation which does not exist in mass, but which appears 

 under the form of veins. The observations already presented 

 on the perfect identity of size in the grain of the vein at its 

 origin, with the grain of the granite mass, and on the gradual 

 diminution which the grain of the vein experiences in propor- 

 tion as it becomes thinner, give a satisfactory answer to the 

 above objection. It may, however, be added that in the gra- 

 nite of Tor-nid-neon, there is not observed those veins of small- 

 grained granite, which are to be found in the granite of Goat- 

 field and of Glen-Rosa. 2d. It has been said that veins of 

 feldspar slightly mingled with mica have been confounded with 

 veins of real granite, (Jameson's Geognosy, p. 108). There 

 exists indeed a mixed rock of feldspar and mica, which, at the 

 first aspect, offers a great resemblance to granite. Such is, 

 for example, the rock described by M. de Saussure, section 1059 

 of his Voyages dans les Alpes, and which forms veins in a 

 foliated petrosilex, near the cascade of Pissevache in the Valais. 

 But the rock of the veins of Tor-nid-neon is a genuine granite; 

 it contains quartz, feldspar, and mica, in the ordinary propor- 

 tion of common granite, and it is only when the vein is con- 

 siderably narrowed that these gradually disappear; first the 

 mica, and tiien the feldspar, when the vein terminates in a slender 



