Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/267

 coal varies from 1,4 to 1,558. There are frequently pins of clay passing through this earthy brown-coal.

I have seen at West Lulworth, another brown-coal passing into pitch coal, in a black loose quartzose sandstone, in which it makes a very thin layer or seam. It hardly burns with a flame, but chars like wood, emitting an empyreumatic or subacid smell. The spec. grav. of the specimen I tried, was 1,340. This last species of combustible matter, as well as the former, is used by the poor people as fuel, and they may be both referred, I think, to the spurious coal of Mr. Kirwan; the range of the specific gravity which he gives, is that of 1,500 to 1,600.

This rock occupies a pretty large extent along the coast: I have observed the four following varieties.

(a) Marl of an earthy semi-indurated texture, which assumes spontaneously polyhedral forms, and contains nodules or kidneys of sulphuret of iron, some of which have undergone a partial decomposition. It has no lustre, the fracture is coarse, the colour of a bluish-grey; it contains numerous specks of mica, it does not effervesce with acids, though the presence of lime is readily shewn by chemical tests; it is composed also of alumina and of a good deal of oxyd of iron; it adheres slightly to the tongue, and is friable when immersed in water, it soon falls into a powder which is rather rough and dry, it decrepitates on the first impression of the fire, becomes hard, and when heated to redness, turns greyish-yellow. It forms a bed of several fathoms in thickness on the south-western coast of the