Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/263



The chalk hills in the Isle of Purbeck lie in the prolongation of a line westward from the Needles: they pass through Corfe Castle, and establish a separation between two troughs, or basins. The one on the north has a gentle slope towards Poole Harbour, the other on the south is more horizontal, extending towards the sea, on the coast of which it presents a range of rather abrupt cliffs. The soil of the latter is very fertile, while that of the former is completely barren, and covered all over with heath.

These hills pass under particular names, such as Nine Barrow Downs, which I found by the barometer to be 625 feet above the level of the sea; Challer Hill, 390; Norden Hill, 369; and East and West Creach. Between Challer and Norden Hills, stands on the top of an hillock, the line ruin of Corfe Castle, the height of which is 207 feet. These hills consist of what is called hard chalk, perhaps from the greater quantity of sand which it contains.

Over the chalk lie several beds or strata of a later formation, the relative age of which I shall not now presume to determine, as their alternation with each other appears to be several times repeated.

I. Flint Gravel in loose Sand or Laom.

This is the formation which prevails chiefly on quitting London, in travelling to the south-west. On the road to Southampton by Bagshot, Farnham, &c. I have traced it as far as to New Alresford;