274 
SILUKIA. 
[Chap. XI. 
these Devonian rocks long after their formation, so must he also admit 
that the change from the red sand and shale of Hereford, Brecknock, and 
Carmarthen to the grey shale with much red sandstone in South Devon is 
by no means abrupt, but resembles the gradual change which begins to 
take place in Pembroke. Nor is there any difficulty in supposing how, by 
a less diffusion of iron, and under dissimilar submarine conditions the 
southern portion of the area of the same sea should have less of the red 
colour and sandy character than the northern. 
But if, on account of lithological differences, some persons should deny 
that the slaty rocks of Devonshire can be the equivalents of the red sand- 
stone and shale of the Silurian region of Hereford and Shropshire, let it 
be recollected that this change in lithological structure is by no means 
more remarkable than the mutation of aspect and character which the 
next overlying (Carboniferous) formation has also undergone in Devon- 
shire ; for in no distant parts of the world do two coal-formations of like 
age present mineral and zoological characters more entirely unlike each 
other than do the rich South- Welsh basin of Glamorganshire and the 
sterile Culm-region of Devonshire, separated only by the Bristol Channel. 
Such variations of mineral character in these deposits are not unknown 
in different parts of the world. 
The great eruption of the granite of Dartmoor, which affected both the 
Devonian and Carboniferous strata in contact with it, has so usurped the 
place of the regular deposits in South Devon that in vain do we look, either 
there or in Cornwall, for the same clear order as in North Devon, where the 
three divisions of this group are clearly recognized, viz. the Lowest or Lyn- 
ton series (Spiriferen-Sandstein, or Systeme Coblentzine, of the Rhenish 
Provinces), the Middle or Ilfracombe series (Lenne-Schiefer, and Eifel- 
Kalk or Stringocephalen-Kalk), and the Upper or Petherwin series (Cypri- 
dinen-Schiefer, Clymenien-Kalk, and Yerneuilii-Schiefer of the Belgian 
area). In fact, the derangement in the western portion of South Devon and 
the adjacent parts of Cornwall is so great that, as already stated, the Lower 
Silurian rocks are seen to overlie true Devonian rocks ! * The metamor- 
phism of some of the schists has, indeed, often given to them the semblance 
of the oldest primary rocks. It is now ascertained that in North Devon 
also much contemporaneous eruptive rock (felspathic ashes &c.) has meta- 
morphosed the slates of the Ilfracombe or Middle Devonian series, — espe- 
cially along the strike of those beds from Combe Martin to Parracombe, and 
on to Stowey in the Quantocks, and also along another line ranging from 
Lee Bay west of Ilfracombe to Kentisbury and Rowley, and along a still 
better-defined course from Woolacombe to West Down, Bittadon, and Gar- 
man Down &c. 
The Quantoek Hills. — These hills of Western Somerset, ranging from 
S.S.E. to N.N.W., are essentially composed of a great mass of the Lower 
H Sec p. 145, and Quart. Journ. Geo). Soc. vol. viii. p. 13. 
