24 Remarks on the Transition Rocks of Werner. 
derstood by the term Elvan; but this is a mistake: elvan 
may sometimes be greenstone, but in general is either killas 
or granite, and is so termed by the miner when he finds 
the rock harder to work in one place than in another. 
Before TI entered Cornwall, I was led to believe that it 
abounded in two kinds of oranite, Primary and Secondary. 
Never having had an opportunity of comparing them in 
situ, 1 was anxious to do so here, and different localities 
were pointed out to me: these I examined with care, but 
eould discover no grounds to justify any distinction. Dr. 
Berger makes no mention of secondary granite ; and an- 
other gentleman, whose opinion on this, as on most sub- 
jects, will be received with the utmost deference, and who 
had the same object in view, during a visit made since I 
was there, informs me that he could discover no distinction 
at all. 
Jt is therefore of importance to ascertain whether the 
ranite of Cornwall be new or old; which will easily be 
anne, by comparing the appearances it presents, with the 
descriptions of these rocks as given in the Wernerian 
school ; it is there taught, that three formations of granite 
have been ascertained. : 
The oldest is the basis or nucleus, round which all other 
rocks have been deposited. The second occurs only in 
veins, traversing only the granite of the older formation. 
The third rests on some of the older primitive rocks, in 
unconformable and overlying position, From this de- 
scription of its external relations, it is evident that the 
ranite of Cornwall can neither be the second nor third, 
Vith respect to its internal structure, we have the follow- 
ing definition: Granite is a granular agevegated rock, com- 
posed of felspar, quartz, and mica. These alternate from 
Jarge to small, and even to very fine granular. The large 
and coarse granular usually belong to the oldest; the small 
and fine grannlar to the newest granite formations, Be-» 
sides’ felspar, quartz and mica, other fossils sometimes 
occur in it; of these, schorl is the most frequent, then 
garnet and tinstone*. 
~ At Penzance [ observed some buildings constructed of a 
remarkably fine-grained granfte; but this | nowhere saw 
in situ: otherwise, from Teign Bridge, where I first set my 
foot on granite, to the Land’s End, it is generally of that 
character which entitles it to be ranked with the-oldest va- 
ricty (Nos. 8, 21, 27, 34, 35, 54, 55.), [nm many places it 
* Jameson's Mineralogy, vol. iii. p. 102, &c, 
has 
