356 Mr. Horner on the Geology of the 



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 how- 

 ever 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 conform- 

 able with the slope of the hill in the lower part of which the con- 

 glomerate 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 



