\ 
94 Remarks on the Transition Rocks of Werner. 
, 
counties of Down and Derry, this rock. lies directly on 
granite,—a circumstance which we should at first sight be 
inclined to cansider as indicating its subsequent formation. 
This thought, however, vanishes the moment we contem-" 
plate the veins of granite by which it is traversed. Of 
these there are many examples; but the most striking are 
at the Louran in Galloway, and at St. Michael’s Mount in 
Cornwall. 
It is many years since Sir James Hall laid before this So- 
ciety an account of his observations on the granite district 
of Galioway, of which the Louran forms a part; and to 
the persevering activity of that gentleman we are indebted 
for the display of one of the most interesting exhibitions 
of granite veins that exists. The peculiarities observable 
in Galloway were first pointed out to me by him; and as he 
has so lately favoured the Society with a particular account 
of them, it leaves me nothing to say regarding that quarter. 
At St. Michael’s Mount, the shooting of the veins from 
the great mass of granite is also most strikingly exempli- 
fied. They were here first noticed by Professor Playtair, 
who compares them, most aptly, to the ramifications of the 
vegetable root *; for, indeed, nothing can be more illustra- 
tive of the phenomenon as it is here exhibuied. 
It is to be observed that granite veins, particularly when 
extremely minute, usually differ in texture from the mass 
to which they belong. While the little peak of St. Mi- 
chael’s Mount maintains a similarity of character with all 
the rest of the Cornish granite, not only in point of internal 
structure, but with respect to the tin and copper veins 
which traverse it, as well as by the massive blocks, hewn 
by the corroding hand of time, which ornament its sum- 
mit; the veins that set off from it gradually become finer 
as they recede, but still preserve the perfect character of 
the rock. 
The importance deservedly attached by Dr. Hutton to 
the phenomena of granite veins, gave rise to a variety of 
hypotheses among those who were inclined to consider this 
rock as the original deposite, who have accounted for their 
formation in different ways. 
It was first stated, that they were formed of newer gra-' 
nite, and, if properly examined, would be found to cut the 
old granite as well as the rock which rested on it. 
This opinion was once very strenuously supported in this 
country; but as facts would not bear it out, it was aban- 
* Illustrations of the Huttonian Theory, p. 318. 
doned, 
