AND ANALOGIES, OF ROCKS. 231 



fluous proof which I did not think necessary to ad- 

 duce, towards the posterior and forcible intrusion of 

 trap and granite into the strata. Such conglomerates 

 are often found at the places where these two latter 

 rocks pass through., or interfere with, the stratified 

 ones ; and that I may quote an instance from foreign 

 authors, and therefore free from the chance of bias 

 on my own part, I shall refer to Canzacoli near Pre- 

 dazzo, where this appearance attends the junction of 

 a mass, which is, at the same time, granite and trap, 

 with the secondary strata. In our own island, the 

 vicinity of Oban offers very extensive and obvious 

 examples. 



There is little now to be said respecting the for- 

 mation of the unstratified rocks, which does not fol- 

 low from the views of their origin formerly held out. 

 Of their materials, we can only know that they are 

 those which are also found in the stratified substances, 

 and can only conjecture, indiscriminately, that they 

 have been formed by the fusion of some or other of 

 these. Differences in the proportions of the several 

 earths are the only grounds of judgment ; and thus 

 it would be inferred that granite was the produce of 

 gneiss, micaceous schist, quartz rock, and, ultimately, 

 of argillaceous sandstones, and that the ordinary 

 traps were the produce chiefly of the argillaceous 

 substances, slate or shale. More particular evidences 

 in confirmation of this opinion, will be found in the 

 histories of trap and granite. But that trap and por- 

 phyry have actually been thus formed, is clearly 

 proved by finding those rocks entangling fragments 

 of schists, in which the gradual melting down of the 

 materials is distinctly traced. The fact itself is de- 

 tailed in its proper place. 



