HORNBLENDE SCHIST. 171 



beds of various dimensions, and under all the usual va- 

 riations. When intermixed with gneiss, which is its 

 predominant association, for reasons already apparent, 

 it follows the contortions of that rock; affording, by 

 its contrast of colour, the most perfect indications of 

 those: and, as already remarked, it is traversed by the 

 same granite veins. Hence, it has been called subor- 

 dinate ; but, as already said, this only proves that the 

 intrusion of the veins was posterior to the deposition 

 of the compound mass. Wherever, like the gneiss it- 

 self, it is unaffected by these veins, all that follows is, 

 that no intrusion of granite has there taken place since 

 its deposition. It is occasionally found among the 

 greater masses of micaceous schist ; while hornblende 

 then sometimes enters into the composition of that 

 rock, so as to produce an intermediate substance. In 

 these cases, other compound and anomalous strata 

 are often present; chlorite schist being frequently 

 among the number. Its peculiar association with this 

 rock has just been described. 



It is occasionally found accompanying argillaceous 

 schist; appearing to pass into the finer clay-slate by 

 an insensible gradation. I have already shown the 

 peculiar interest attached to this transition at the con- 

 tact with granite; particularly remarkable where its 

 veins traverse clay-slate, or whcse fragments of the 

 latter are entangled in it. From this fact, and the pa- 

 rallel ones at the contact of shales and trap, it would 

 appear, that the fusion of clay-slate, whether primary 

 or secondary, is, under various circumstances, ca- 

 pable of generating, either the common trap rocks, or 

 the hornhlende schists : nor is it perhaps difficult to 

 explain, by a more gradual cooling, and consequently, 

 a slower crystallization, the particular causes which 

 . may have determined the latter rather than the former 

 effect. Instructive examples of this transition occur 



