Affinity between Bajaltes and Granite . 5 x 
of any bias towards fuch an hypothefis. The firft ftep in 
the progreftion appears at the Giant’s Caufeway in Ireland. 
Many of the pillars there confift of fine- grained, dark-coloured 
whinftone ; that variety which may be confidered as mod 
perfe<ft, and as equidiftant from porphyry, petrofilex, and 
granite; but at the promontory of Fairhead, the character of 
the done is feen to alter, and it has lately been defcribed as an 
imperfect kind of granite Hence we are led by regular 
approaches to perfect prifms of granite, accompanied by prifms 
of common whinftone, and not lefs obvioufly than the dif- 
ferent ranges on the Coaft of Antrim betraying a common 
origin. The pillars of Les Rameaux, though they rather 
incline towards the dark colour and uniform hard fubftance ; 
yet, when broken, are unequal both in colour and texture, 
46 and fometimes interfperfed with irregular pieces and patches, 
“ as it were, of an heterogeneous hard fubftance, which, by 
“ its micas and fmall rhomboidal cryftallizations, much re- 
“ fembles a fort of granite I have frequently feen* The 
“ mafs on which thefe columns ftand is of the fame mixed 
(6 character Other examples will occur afterwards; and 
for bafaltiform colonnades of granite it is only neceflary to 
refer to Mr. Strange’s defcription of Monte Roffo The 
general fhape of the Euganean hills, as if fuddenly raifed by 
* Hamilton, 2d edition of his Letters, p. 37. fays, it “ refembles an imper- 
fect compaCt granite.” I have fpecimens from an hill near Mallwhyd, in the vicinity- 
of Cader Idris, where the texture infenfibly changes from an uniform whinftone 
ground to grains of mica, feldfpath, ftioerl, and, I think, fometimes quartz. 
They are, I fancy, like thofe denfe lavas of Etna, “ Qui, vues a la loupe, laiffent 
appercevoir des ebauches de cryftallization de fhorl, de quarz, ou dc feld-fpath. 
Dolomieu, /. c. p. 182. 
t Strange, Phil. Tranf, LXV. p. 13. 
X Ibid. 
H 2 
the 
