Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/268

 Isle of Wight, where it lies between a stratum of loose quartzose sand, and one of calcareous freestone with chert, above the source of an alum chalybeate spring. It is found also to the north-east of Alum bay, where it alternates with sand; at High cliff in Christchurch bay, where it constitutes most part of the cliff, and is covered only by the flint-gravel; and between Encombe and St. Aldham's Head in the Isle of Purbeck.

(b) Marl of a bluish-grey colour, intermixed with iron-pyrites. It has a degree of lustre, its texture is slaty, it feels smooth and greasy, does not contain mica, and is not acted upon by acids; it falls in water into a very fine powder, but not so readily as the former variety: when heated it becomes harder, of a yellowish colour, and its structure appears more evidently foliated. I have observed it in the bed of a rivulet which runs to the sea near Compton-field, on the west-south-western coast of the Isle of Wight, not far from Brixton bay. The flint gravel lies over it.

(c) Marl of a greyish-white colour, harder than the two former varieties, effervescing with acids, and adhering more strongly to the tongue. In water it does not fall into powder; the fracture is earthy ; no specks of mica are visible in it; when heated to redness it does not decrepitate, but becomes harder, and of a reddish-brown colour. The surface is often covered with compressed nodules of sulphuret of iron; it alternates with the preceding kind.

(d) Marl of a bluish-grey colour effervescing with acids; its fracture is dull and earthy; it contains a great many shells and a few specks of mica. In water it does not fall into powder; it hardly adheres to the tongue; when heated, it decrepitates slightly, and the texture becomes more evidently slaty ; by a red heat it acquires a white-reddish tinge, and gives out a bituminous smell analogous to that of the Kimrridge coal, or to express myself more