regarding the Rochs of the Red Sandstone Formation, 81 
sition, as the trachy tic mountains ; but if the porphyritic masses 
have been but small, they form only nearly vertical, cylindricalji 
or wedge-shaped masses, like the submarine basalts of Eisenach^, 
Moravia, Hungary, &c. 
Porphyries are dtiiate in hillocks, associated with some kinds 
of porphyritic streams or protuberances, upon primitive and 
transition rocks, upon the coal sandstone, upon the todliegende 
or newer red sandstone, and upon the first floetz limestone. All 
these formations are traversed by porphyry veins, or cylindrical 
bodies of the same rock, as is so clearly seen in Scotland, the 
Erzgebirge, the Alps, &c. ; here and there only the veins have 
accidentally formed short beds or imbedded masses in the Nep- 
tunian deposites. 
Lastly, porphyries are often connected with sienitic and gra- 
nitic hills, or immense cylindrical or v/edge-shaped granitic 
masses or districts, and sometimes include more or less consider- 
able portions of older rocks, in some instances elevated, or dis- 
located, or even altered. Ben-Nevis, the highest mountain itf 
Britain, presents such a connection with sienite ; and Dr Mac- 
knight’s characteristic description of that hill and its neighbour- 
hood testifies most amply its igneous elevation. 
After adducing all these facts, which I look upon as of a 
very superior kind, I might conclude these pages with nearly 
the same words as Mr Beudant, did I not think them rather 
too strong ; and yet, for the benefit of science, while, at the same 
time, I have no inclination to diminish the high degree of credit 
which my opponent so justly deserves, I shall here transcribe 
his conclusion. 
After all these facts,” says M. Beudant, which I look 
upon as of a very superior kind, I am of opinion that none of 
the observations which have hitherto been adduced as tending 
to the adoption of the igneous (I might say aqueous) origin of 
the felspar and basaltic rocks of the red sandstone, even allowing 
them all the weight which they have not, could prevail over cir- 
cumstances of position, so generally diffused in nature, and so 
well established by the great majority of geologists.” 
If, after the exposition of similar facts, the igneous (I might 
say aqueous) origin is still to be admitted for the crystalline 
rocks subordinate to the coal sandstone or the red sandstone, k 
VOL. X. NO. 19. JAN. 18.^1 
F 
