Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/205

From Wikisource
Jump to navigation Jump to search
This page has been validated.
Mr. Webster on the Strata lying over the Chalk.

septaria: in these the shells often retain their original pearly lustre. The nautili are particularly fine.

Boughton hill, between Feversham and Canterbury, consists of the London clay. Still nearer to Feversham fossil shells are found, which are entirely siliceous. They lie loose in a thin bed of greenish siliceous sand that occupies a situation lower than the blue clay, and are separated from the chalk by a thick bed of yellow sand. Mr. Crow has collected here the strombus pes pelecani, a murex, a species of cucullea, and several other bivalves.

One of the most interesting sections above the chalk is to be seen at Woolwich, near the banks of the Thames. At this place the junction of the chalk with the strata over it is plainly to be seen. Over the chalk is a stratum about 30 feet thick of very fine white sand; and towards the top there is a thin bed of clay. Next succeeds a stratum of about 10 or 12 feet, composed wholly of flint pebbles, which have been worn by water into their present forms, and lie in the utmost confusion piled on each other, having a vast number of fossil shells lodged in the interstices.

The whole has the appearance of having been at some period a heap washed up on the sea shore, similar to our modern beaches. The shells are entirely whitened, and having lost their animal matter, are extremely brittle: their species however may be in general ascertained, although very few are to be found entire. They have been already described by Mr. Parkinson.

The bottom of this stratum of pebbles is now about 30 feet above the level of the sea. Over this is a layer of sand with some ferruginous masses, and then several thin strata of clay alternating with sand. In this clay are vast numbers of bivalves, locked into each other so close that this must doubtless have been their original bed.