The Rev. D. Williams on tlieGeology of Devon Sf Cor?iwalL 61 
south-west of Callington, with those which had been pro- 
cured from the fine culm shales near Bideford. I believe it 
to be an impossibility, on account of the same coarseness of 
the matrix in the great outlier, as exists everywhere, that I 
have seen, in the rocks of the floriferous series generally, 
where I have never met with clearly defined specimens, ex- 
cept in the finer culm-shales just mentioned. All I am pre- 
pared to prove then is, that about St. Mellion and Pillaton, 
between Callington and Plymouth, plants in the same imper- 
fect condition are found in precisely the same slates and 
shales, vohich are parted by thick beds of the same sandstone, 
and in intimate association voith that singidarly characterized 
and unique formation the Coddon Hill grit', there is the same 
triple association of the same rocks, and in the same order of 
succession, that we witness in the base line of the floriferous 
series along the north and south borders of the trough, and 
where on earth could they come from if not from the same 
sources which supplied the constituents of the same rocks 
elsewhere in the same county ? The only deviation on the 
S. and S.W. of Callington from the normal types of the flo- 
riferous series elsewhere, is frequent intercalations in it of 
undoubted killas, and beds of a composite or neutral charac- 
ter, constituted of moieties of killas and Coddon Hill grit, or 
of killas and floriferous, round the confines of the outlier 
seen not only in repeated alternation, but in other instances, 
their wedge-shaped extremities interlocking into each other 
like the teeth of a rat-gin. Here, as elsewhere along the con- 
fines of these two vast formations. Nos. 9 and 10, whether 
we advance towards the floriferous area on the one hand, or 
towards the killas on the otlier, we distinctly observe the one 
becoming thinner and evanescent as the other augments into 
unity and fulness. 
Nature has manifestly conducted her operations of deposi- 
tion and elevation in this region on a vast scale, and if her 
works be not regarded in their just proportions, we never 
shall arrive at the truth : thus as we explore the confines of 
Nos. 9 and 10, we are startled almost at the vastness of the 
ties and adjustments by which they are indissolubly united, 
till we reflect that they are only in a ratio to the magnitude 
and dimensions of their respective masses ; that it is only the 
same transition and alternation on a larger scale, that we ob- 
serve throughout Exmoor between the several members from 
No. 2 to No. 9, on a smaller ; for while I hesitate as to the 
diameter of No. 9 ; No. 10, I repeat, is upwards of eight 
miles, measured according to Professor Playfair. Thus again, 
if we take a coup d'ceil view of this country from one channel 
