424 



Remarks on the 



[June, 



church. There can he no doubt that this singular rock owes its 

 present appearance to the operations of time on the surrounding 

 materials, which its peculiar composition has enabled it to with- 

 stand. 



The killas likewise presents marks of degradation where the 

 country is composed of that rock. 1 noticed in some districts 

 the roads mended entirely with quartz ; the brilliant -white ap- 

 pearance of which, after a shower, had a very curious effect. I 

 could not comprehend by what industry the accumulated heaps 

 of this substance were obtained : at last I perceived that they 

 were gathered from the adjoining fields, and in some places 

 picked from the surface of a common, by means of a hoe or 

 mattock. That fragments of quartz should occur so unmixed 

 with any others is only to be accounted for by supposing that 

 they formed the quartz veins in the killas, which, from superior 

 tenacity, resisted decomposition; while the softer parts of the 

 rock, yielding to the action of the weather, were reduced and 

 carried away. 



We thus find that the granite of Cornwall possesses the cha- 

 racters ascribed by Werner to that of the highest antiquity. 

 Some inferences may likewise be drawn in corroboration of its 

 title to be classed with rocks of this description, from the nature 

 of the metallic veins by which it is traversed. In the German 

 account of the relative ages of metals, tin is the third, and wol- 

 fram the fourth, in order of antiquity.* If veins containing 

 these metals be considered in other countries as indicative of 

 rocks of the oldest primitive formation, the same appHcation 

 must be made to those of Britain. 



I may now ask, if this be not the oldest granite, where are w^e 

 to find it ? ^s it appeals to me impossible that any substance can 

 more decidedly concur with definition. In the Alps, Dr. Berger 

 must have learnt what primitive granite meant ; yet not a doubt 

 escapes him of the Cornish being any thing else. Distinctions 

 either do or do not exist : if they do, character must be attended 

 to; if they do not, it is quite unnecessary to add the terms 

 secondary and tertiary to a substance possessing every attribute of 

 a prin'iary variety, merely because the structure of an adjoining 

 rock does not accord, with a specific theory. 



Graywacke, or, as I shall in future call it, killas, I have be- 

 fore noticed, is a rock composed of fjcagments more or less com- 

 minuted, which must have existed in another state before they 

 assumed their present arrangement. Along with the strata 

 formed of these, beds of limestone are found, containing indi- 

 cations of organic remains. These are not confined solely to tbe 

 limestone, they occur also in the killag ; a fact which may be 



* Jameson's Mineralogy, vol. iii. p. 275. 



