GEOLOGICAL FORMATIONS NEAR DUNSTER. 143 
isolated ; for while the hill itself belongs to the Devonian 
series, its base is surrounded by the red sand-stone de- 
posit. 
The special object of this paper will not admit of our 
entering on the probable extent of surface over which the 
seas of the New red sand-stone extended. We must, there- 
fore, confine our observations to that portion which belongs 
to this immediate neighbourhood. Most of the character- 
istie features which distinguish the series present them- 
selves in this locality. We have the conglomerate, into 
the composition of which fragments of the rocks composing 
the neighbouring hills enter largely. We have the finer 
detrital matter, in the form of sand, held together by a 
natural red ferruginous. cement, and the various grades 
and shades between these two. We have the red mal, 
which forms so striking a feature in the agricultural aspeet 
of our large valleys. And as in the Devonian, so likewise 
in the red sand-stone, we have streaks or bands of lime- 
stone. The cementing matter of the conglomerate lime- 
stone contains so large a proportion of magnesia as to 
obtain the name of magnesian lime-stone. In some places 
it contains rounded fragments of the Devonian rocks, 
united in one solid mass by a magnesio-calcareous cement, 
thus clearly indicating its origin and the circumstances 
under which it was formed. 
The lower beds of the red sand-stone series are 
peculiarly interesting in this neighbourhood, from 
their affording in great purity the only truly precious 
metal of our country—I mean iron. If you refer to 
the Geological Map you will observe that during the 
time the red sand-stone was deposited, a gulf of the sea 
must have occupied the opening at Porlock, skirting Luc- 
combe, and flowing up as high as Timberscombe. At the 
