IV.—Observations on the Purbeck and Portland Beds.

Abstract

The following communication is the result of a short visit which I paid to the Isles of Purbeck and Portland some years ago, subsequently to the publication of my Letters to Sir H. Englefield. In that work I traced out the great features of this very interesting district; but a detailed account of the beds is yet a desideratum. To supply in the mean time some materials for such a purpose is the object of the present paper. I shall confine myself here to the beds which furnish the well-known Purbeck stone, which is extensively employed in London for the side pavement of the streets; and to the beds in the Isle of Portland from which the principal material for our public buildings has been procured. The beds in the northern part of the Isle of Purbeck are considerably inclined; they dip to the north, coming out to the day from under a series of clays and sandstones which are the equivalents of the Hastings beds described in a former paper. The situation of all these, and their relations to the chalk, are well seen in Swanwich and Durlstone Bays, in the east end of the Isle of Purbeck, and in Warbarrow Bay on the west. Their general direction being from east to west, a very instructive section of the limestones usually known by the name of the Purbeck Beds may be advantageously studied in the latter of these places. A line of elevated ground, consisting of these calcareous strata