File:The Quarterly journal of the Geological Society of London (12895303584).jpg

152
PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .Feb. 3,
This " Crab rock," as seen in the section, is in some parts twenty
feet thick

but its thickness is very irregular as it spreads over
the eroded edges of the Carboniferous Limestone. It is seen, not
only reposing unconformably upon the Carboniferous rocks, but also
enclosing veins of haematite (see fig. 3). Another locality where
this breccia or " Crab rock" appears is St. Helen's, about half a
mile to the north of the Park cutting, and immediately east from
the railway. Here the Carboniferous Limestones have the breccia
also spread out upon their surfaces, and into some of the open joints
which intersect the underlying strata the " Crab rock" has found its
way. At Dalton the same relations occur. Near the church the
" Crab rock," consisting of unaltered fragments of limestone cemented
together by a red matrix, also covers over the Carboniferous strata.
This " Crab rock" is well known to miners, who have noticed that
where haematite occurs below it, in the Ulverstone district, the latter
is always in intimate relation to the former.
Fig. 3. — Section from Park to Furness Abbey (11 mile).
is r .
Park.
Breccia
'Crab rock.
Furness
Abbey.
12 12 1 3
1. Carboniferous Limestone.
2. Haematite.
3. Fault.
4. Corby Sandstone.
With reference to the position of the " Crab rock," its mineral
characters lead to the conclusion that it is of like age with the lower
and unaltered breccias of Burrells, west of Appleby

for it possesses
none of the magnesian features appertaining to the higher breccias.
Here, therefore, the lowest Permian rocks of the north-west of
England are seen

and after the clear and unmistakeable natural
section at Barrowmouth, under St. Bees Head, where the Lower
Permian is reduced to a few feet in thickness, we have no occasion
to call in the agency of great denudation in the Furness district.
In truth, it is quite manifest that along the western flank of the
old slaty mountains of Cumberland we meet only with ridges or
patches of Carboniferous Limestone, which, with the exception of the
very partial breccias above described, are at once surrounded by the
middle and higher members of the Permian group, of which hereafter.
d. Hcematite in the Lower Permians. — The mode in which that
valuable ore of iron, hcematite, is found deposited in pre-existing
cavities of the Carboniferous formation, and sealed up by " Crab
rock," is a matter of great geological interest. Joints, fissures, and
caverns were doubtless formed in the older rocks antecedent to the
deposition of the Permian strata, and in these the ores of iron so
widely diffused throughout the Permian rocks have, in this portion
of the north-western region, assumed the characters of