component parts are large, as in the conglomerates, the nodules consist of some of the varieties of rock that compose the grauwacke formation; and in many places there are nodules of a limestone very similar to that of the subordinate beds in the same series. These derivative rocks under one form or another are found in all the intervening valleys, and the great valley on the western side of the Quantock hills is wholly composed of them. They are not however confined to the vallies, but are sometimes found on the sides of the hills at a very considerable elevation. It would have been a fruitless task to have attempted to distinguish in the map each particular form of aggregation, more especially as I did not discover any uniformity in their relative positions. I have thought it better to class the whole under one head and to represent them as such by one colour. It will be necessary however to point out in detail some of the most remarkable instances.
§ 21. In the eastern and highest part of the valley in which the village of Porlock is situated, there is found at Tivington, Huntsgate and Holt farm, a conglomerate composed of thin fragments of a coarse grained slate seldom exceeding an inch in size, with pieces of quartz, cemented by white calcareous spar. The surfaces of the fragments are rounded by attrition, and are coated with reddish brown oxide of iron, which has in many places the metallic lustre of hematite. The fragments are in some places so small that the rock has the appearance of a sandstone. It occurs in thick beds which are often inclined at a considerable angle, but not conformable with the slope of the hill in the lower part of which the conglomerate is found. The smaller grained rock frequently alternates with the coarse conglomerate: at Tivington the latter variety prevails, but at Huntsgate that resembling a sandstone forms the thickest beds. Both varieties are very much traversed by veins of calcareous
