Scientific Reviews. 121 
granites. 4. Whitestone, (Eurite.) 5. Granite posterior to gneiss. 
6. Granite posterior to mica slate. 7. Granite and gneiss posterior 
to clay slate, (Kielvig and Shetland islands.) Now while Dr. Ure 
does delineate some of the mineralogical features of this most im- 
portant rock, he merely alludes to its alternation, premising after- 
wards, that “‘ veins which proceed from them, traverse the adjoin- 
ing rocks, together with those similar veins which, though of the 
same mineral-composition, cannot be traced in the same manner to 
a fountain head,” and consequently that they must be “ included 
among granites.” Does this inform us that this very fact is of pri- 
mary importance in the deductions we should form of the relative 
age of the mother rock? Is the vein or the rock pierced? Veins of 
granite in granite, or veins of granite in gneiss? Are such facts of 
no importance? The occurrence of granite on rocks of posterior for- 
mations, is appurently no where mentioned. Professor Brande has 
searcely at all troubled himself with the subject, and thus it is that 
foreigners have to visit the mines of Cornwall, that we may be- 
come acquainted with the age of rocks worked from the time of the 
Pheenicians, (Dechen and d’Oenhenosen in the Annals of Philoso- 
phy,) and the same remarks will apply to descriptions given of the 
whole of the inferior order of rocks in these two works. 
“ A rock with more or less of a slaty texture, but distinguished 
from slate by its less perfect lamellar fracture, and above ali by its 
imbedded fragments, and being, at the same time, essentially argil- 
laceous, appears to constitute legitimate greywacke,” says the Pro- 
fessor in page 114, while Dr. Ure designates greywacke as “a rock 
commonly composed of grains or fragments of quartz and Lydian 
stone, among which bits of clay slate are disseminated. These parts 
are agglutinated by a cement of an argillaceous kind, usually im- 
pregnated with coarse siliceous matter. The size of the grains of 
quartz and Lydian stone, rarely exceeds a nut, but the pieces of 
clay slate are sometimes as large as the hand,” (p. 141.) Now if 
we told our readers that greywacke is a name given to those depo- 
sits, of heterogeneous composition, which occur between the last of 
the primitive rocks, and between transition slates and porphyries, 
and the old red sandstone, zechstein, and coal formations, and that 
they are one of the first strongly marked, partly mechanical, partly 
chemical deposits, we think they would be able to form a better 
idea of the probable character of such a formation, than by compar- 
ing the discordant evidence of two systematists, and would thus be 
prepared better to comprehend how, in the Lammermuir range of 
hills, the fragments becoming so comminuted as to be no longer 
discernible, the rock takes there a schistese texture, approaching 
to clay slate, a fact with which Dr. Ure seems, however, to have 
been slightly acquainted ; or may at the foot of the slates of South 
Wales, or the granite of Malvern Hills, present the feature of huge 
boulder stones, many feet in diameter, imbedded in an argillaceous, 
and oftentimes coarse silicious cement. This might be called grey- 
wacke passing into conglomerate ; but it would be naming similar 
VOL. I. Q 

