q§. Mr. Mills’s Objervatiom on 
holes ; whilft in other parts they are filled with a cryftalline chert, 
with which the tops of the neighbouring mountains, and the 
Paps of Jura, abound: in Ihort, from the very rude and irre- 
gular appearance of the fummit of the hill, from its rifing fo fud- 
denly from the limeftone ftrata, and from the Whyn Dyke 
which runs through it, and which may be traced ranging far 
away to the north- eaft ward, I am ftrongly induced to believe 
it of volcanic origin. 
If it be admitted that I am right in my opinion of the vol- 
canic origin of thefe different fubftances, a large trad will 
then be added to that already proved by others to have been 
fubjed to the effeds produced by fubterraneous fire ; which, as 
far as has hitherto been difcovered with us, commences in tiie 
S.W. part of Derbylhire, and, if I miftake not, is again feen 
in Seathwaite, about five miles from Hawklhead, in the N.W. 
part of Lancafhire, and appears (N.W. from thence) in the 
neighbourhood of Belfaft in Ireland, and ranging through the 
northern part of that kingdom ; it is perceived in feveral of the 
weftern iflands of Scotland, extending as far north as tne 
ifland of Lewis, which is the northernmoft of the Hebrides, 
and croffing eaft from Hay (which is the fouthernmoft) by 
Tarbut, Dumbarton, Stirling, and Edinburgh to Dunbar. 
Some perfons may confider, with aftonifhment, the extent 
of thole veins and mafies of lava which appear in the northern 
part of the Britilh ifles, where no crater is vifible ; whilft 
others, who have read Von Troil, and recoiled that he fays 
(at p. 234*), “ That lava is feldom found near the opening of 
“ a volcano, but rather tuff, or loofe alhes and grit,” may per- 
haps unite with me in opinion, with Mr. Whitehurst, 
that the crater from whence that melted matter flowed, to- 
“ gether with an immenfe trad of land towards the north, 
“ have 
