Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/196

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Mr. Webster on the Strata lying over the Chalk.

and thickness. They extend quite across the island in a vertical position, keeping parallel to the chalk, and appearing again at White-cliff bay on the east end, where they are however much concealed by grassy slopes.

All along the north side of the range of chalk hills which extends from Handfast-point through Corfe Castle, there is an extensive stratum of pipe clay in a horizontal position. It contains a bed of coal so exactly resembling that of Alum bay, that this circumstance, added to the quality of the clay and its geognostic position, is sufficient to identify it.

I have been favoured by Alexander Jaffray, Esq. with the following section of the clay pits of Norden, near Corfe.

Sand on the top 10 feet
Blackish brown clay 14
Wood coal   3
Refuse clay   5
Fine white potter's clay   6
Dark brown clay   2
Fine white potter's clay   6

The same stratum of clay, though not of equal quality, may be traced in the hills near Poole; and is found in many parts of that extensive tract called the trough of Poole.

Potter's clay, white, yellow, or greyish white, similar to that in the Isle of Wight, is also frequently found in the London basin: some of it is of considerable fineness, as on the east bank of the river Medway, near Rochester.

The plastic clay is frequently of a deep red colour, or red and white mottled, as in Alum bay: a similar red clay is dug near Portsmouth and other places along the South Downs. It also appears at Reading.