186 PROCEEDINGS OF THE GEOLOGICAL society. [Dec. 15, 
A. Planking, 10 feet, usually consists of several beds; a shelly, 
coarse calcareous sandstone, having oolitic globules im parti- 
cular layers, but upon the whole sparingly distributed. These 
beds are sometimes very hard and barren of organic remains ; 
in other situations again they are distinguished by a profusion 
of relics, including many zoophagous Trachelipods, which seem 
peculiar to the great oolite. The partings of the beds frequently 
exhibit a remarkable appearance ; the shells, for the most part 
broken, are piled im diagonal layers, so as frequently to con- 
stitute a large proportion of the mass of the rock, together 
with rounded fragments of harder sandstones, coralline bodies, 
crabs’ claws, palates and teeth of fishes, remains of Pentacrinite, 
Ophiura, spines of Cidaris, &c. Other blocks will be found 
strewed with small spiral univalves belonging to the genera 
Cerithium and Nerinea. The structure of the shells consists 
of pure crystallie carbonate of lime, and their internal cavities 
are frequently filled with the same substance. From this crystal- 
line structure the stone appears to derive its superior hardness 
and durability ; when once dried by exposure to the sun it does 
not readily absorb water and consequently resists the action 
of frost. The largest blocks are worked into pillars, gate- 
posts, trough-stones, and other uses where much exposure is 
required. 
Beneath the planking sometimes succeeds a few inches of 
sand or brown clay, and it may be remarked that the bivalve 
shells in this and other clay seams, unlike the stony beds, have 
usually both valves in apposition, though for the most part in 
the form of casts. 
B. Soft, yellowish sandstone, thin-bedded, 12 to 14 feet, divided 
occasionally by sandy partings. ‘These beds are worthless for 
economical purposes, the absence of shells and crystalline lime 
rendering it liable to destruction from frost, which, together with 
its small masses and tendency to lamellar separation, preclude 
its employment for building; it is accordingly suffered to dis- 
integrate on the banks of the quarries. 
C. Soft yellowish sandstone, shelly, 6 feet, much more coherent than 
B, and advantageously worked for purposes where hardness is . 
not necessary ; it is therefore sawn into ridge-tiles and copmg 
for walls. The shells increase in quantity downwards; both 
this bed and B exhibit numerous holes bored by the Lithopha- 
gidee, in some of which Lithodomi may still be found. ‘ Oven- 
bed’ is the workmen’s term for these strata. 
D. Weatherstone, 6 feet, separable into two or three beds ; greyish- 
brown sandstone, abounding with shells and carbonate of lime ; 
the hardness increases downwards until we arrive at the lowest 
bed. 
E. Lowest weatherstone, 6 to § inches ; a coarse, grey, shelly lime- 
stone. The superior hardness of this bed is due to the valves 
of small oysters, chiefly O. acuminata; these m fact constitute 
the greater portion of its mass ; it strikes fire with the tools of 
