Transactions of the Geological Society, 1st series, vol. 4/On the Strata at Whorlbury Camp
X. On the Strata at Whorlbury Camp, in Somersetshire.
By GEORGE CUMBERLAND, Esq.
honorary member of the geological society.
WHORLBURY CAMP is a considerable Roman station situated
just above Weston-super-Mare on a high and well defended promontory
that projects into the Severn sea. At the foot of the
promontory, and at its northern extremity, is a small island, connected
to the main land by a bank of rocks, and always accessible
at low water. The island contains about three acres of green sward,
the remainder of the surface consisting of limestone rocks, which
are deeply excavated. It serves during the sprat season as a place
of resort for fishermen, who have extended their sprat-bangs from
the island to the main land.
A narrow horse road forms the descent from the downs in the
island to the level of the sea, and it is just where the road begins to
quit the sward on the left hand side opposite the sea, that a narrow
stratum of soft red sandstone appears. This sandstone is of the
consistence of schist at its surface, and has its laminæ divided by a
hardened ochreous marl. Its whole thickness is about 6 feet, and it
dips at an angle of about 47°.
In the marly part of this stratum a fossil is found resembling a cane or jointed bamboo. It is rarely obtained more than five inches long, generally curved, but sometimes straight, and of all degrees of thickness from a quarter of an inch to five inches. These fossils lie in great disorder, and are apt to separate at their joints on extracting them from their matrix; and many appear to have had their joints separated as they lay in the sandstone, the ends of the joints being covered with a thin coat of quartz. Many of these fossils have their hollows between the joints filled with hard sandstone, but the greater part have their centres quite filled with the hardest white quartz; and where there are cavities, which rarely happens, they are sometimes found to contain crystals of calcareous spar.
When I first discovered these fossils, ten years ago, I found them upon the beach just under the sandstone rock, and took them for corallines; but having since found them abundantly in situ, and examined a number of them more minutely than before, I am induced to regard them as juncous bodies. I know not at least how to class them as corals, since they have not the smallest trace of any passage from one joint to another. Should they be ranked however among the coralline bodies, they must be allowed to be of a very singular nature.
Below the beds containing these fossils a grey limestone is found, in which no traces of marine bodies appear.[1] On the top of this limestone is a thin bed of very yellow marl, and then a thin bed of purple and blue marly earth. Then appears the red sandstone containing the cane fossils, six feet thick. Above it is another bed of blue and purple marl about three feet thick, and above that a considerable bed of limestone of a reddish grain, over which is found a bed of compact red limestone, without fossils. Above this is a vast mass of coarse limestone without fossils, and beyond it many considerable strata of grey limestone, succeeded by others that are thin and exhibit on their surfaces, when exposed to the action of the sea, some traces of the fossil I have been describing.
Just above the ends of the strata that contain the cane fossil, which at the distance of a few feet would have cropped out on the sward of the downs, there is found a mass of a partially indurated pale yellow sandstone, separated into strata by thin layers of sand. This sandy mass is in part soft, and in part indurated, and contains cavities filled with loose sand. It dips at a very small angle in a direction opposite to the strata which contain the cane fossil, and lies upon the ends of these strata as sand would lie that had been thrown over them by a stormy sea. It seems no where more than a foot thick, and is covered with limestone rubble to the depth of two feet, upon which reposes the turf.
In this sandstone are long stalks of alcyonia, resembling those at the back of the Isle of Wight, but the mass in which they are found being of inconsiderable size, I have not been able to find in it any heads or roots of that fossil. These stalks are white like lime, and although in general much decomposed, exhibit their cylindrical forms very exactly, and if taken in fragments look like carious bones.
I observed in a broken piece of the sandstone upon the horse road
already mentioned, a stalk of the alcyonium about two feet long,
and branching at one extremity. I also found among the rubbish
other fragments of stems, which must have been of considerable
magnitude.
The under part of this thin bed of sandstone is stalactitical, forming friable concretions of sand, dependent chiefly from the stems of decayed alcyonia. Were it not for these alcyonia, and for the limestone rubble which is found upon the surface, any one would suppose this bed to be of very recent production, formed of sand and ochre concreted by the action of the sea.
- ↑ Upon the summit of the hill at Uphill (which forms the point of the bay of Weston opposite to Whorlbury) the canes are found in a coarse grey limestone, and may be observed on the same spot in the stones of a mined mill accompanied by small shells of the winged anomis.