Remarks on the Transition Rocks of Werner. 97 
Tn the theory of Dr. Hutton, we find also some grounds 
to account for the diminution of grain in the substance of 
the veins. The same cause to which, in a former paper, I 
attributed the gradation in the texture of greenstone, may 
be supposed to have acted here. It does not, however, ob- 
serve an equal constancy, some veins of granite being as 
coarse-grained as the mass to which they belong. 
In a tormer part of this paper, I had occasion to notice 
an alteration which appears to take place in the texture of 
killas, when in the vicinity of granite. This circumstance 
was so remarkable in Galloway, at the Louran and other 
places, that I took the strata so situated for mica-slate, al- 
though I had observed no line of separation between it and 
the killas. I was forcibly struck with this at the moment f 
but having then no time to follow it up, I was obliged to 
leave the country without any particular examination. It 
will be observed, by the specimens from St. Michael’s 
Mount, that the killas there assumes the appearance of fine- 
grained gneiss. At Wasseldale Crag, between Kendal and 
Shap, I noticed a rock, in the immediate vicinity of granite, 
quite similar ; and I am told that the texture of the strata, 
near the granite of the mountains of Morne, is altogether 
the same. 
This alteration is always of a gradual nature; and is so 
imperceptible, that it affords a good example of what might 
be understood by the German term Passage, or transition 
from one species to another: this Passage, even admitting 
the substance altered, is of too limited a nature to consti= 
tute a distinct and totally different rock. 
This alteration, if traced with attention, may lead to some 
very important results; but, without entering upon it at 
present, I shall content myself with recommending it to 
the notice of geologists, some of whom may consider it of 
too minute a nature to deserve attention. They may, how- 
ever, rest assured, that it is only by an accurate examina- 
tion, and a faithful detail of such oodjects, that we can hope 
to arrive ultimately at truth, the only solid basis of philo- 
sophic inquiry, 
{ may be accused of generalising too much in the fore- 
going statement, on grounds so limited: it must be re- 
membered, however, that [ have purposely confined my- 
self to the examples of the relations which exist within my 
own knowledge, between the transition rocks and granite. 
The same phenomena are familiar, where gneiss and mica- 
alate come in contact with that rock; but as these strata 
are considered to be of a very different age, the facts which 
Vol. 42. No, 184, August 1813, G [I might 
