Vol. 6$.^ INL1ER IN THE EASTERN MENDIPS. 233 



(2) The normal Tuffs. 



These show a considerable amount of variability in character. 

 The following types may be distinguished : — 



(a) Tuff of moderate coarseness, with fragments ranging up to a length of 



three-quarters of an inch. This type is best seen in Sunnyhill Quarry, 

 where it forms Bands 3 & 5 and part of 1. Sections of this rock show 

 andesitic fragments of various types mingled with felspar-crystals 

 and occasionally small pieces of sandstone. This type grades into 

 (b) and (c). (See PL XVIII, fig. 3.) 



(b) Felspathic tuff. This is the type of rock from which many of the 



fossils found near Tadhill Farm were obtained. It consists of 

 andesitic fragments and broken crystals of weathered felspar in fairly- 

 equal proportions. (See PI. XVIII, fig. 4.) 



(c) Fine yellow ash. This forms the bulk of the soft and generally much- 



weathered material of Band 1 in Sunnyhill Quarry ; it is also 

 the prevailing and most fossiliferous type of rock cut through by 

 the trench and thrown up from rabbit-holes south-west of Tadhill 

 Farm. It consists mainly of small andesitic particles. 



(d) Fine red ash and ashy clay, with or without larger ashy particles. 



This type of rock, which has already been somewhat fully referred to, 

 is met with only in Sunnyhill Quarry, where it forms Bands 2 & 4. 



In all these tuffs the great majority of the fragments, though 

 showing a certain amount of variability in the size and relation 

 of the felspar- and pyroxene-phenocrysts and in the presence or 

 absence of vesicles, are of the same general type of pyroxene- 

 andesite as the associated trap ; some, however, are more basic. 

 In some cases, the fragments are converted into green palagonite. 

 Sometimes the rock consists entirely of trap-fragments, or of 

 fragments mingled with felspar-crystals which were no doubt 

 derived from the same source as the fragments ; but, as a rule, 

 there is a certain amount of sedimentary material present, some- 

 times definite fragments of sandstone, more often quartz-grains. 

 In no case is there any sign of a calcareous matrix, such as 

 characterizes the (probably) contemporaneous tuffs of the Tort- 

 worth district 1 and the neighbouring Carboniferous tuffs of the 

 Weston-super-Mare district. 2 



(3) The Coarse Ashy Conglomerate. 



As has been already noted, the rock forming the vast majority 

 of the blocks is the trap or lava of the district, and its characters 

 have already been described. There is however, especially in the 

 area to the south-east of Moon's Hill, a very considerable proportion 

 of non-igneous matter — quartzite, grit, and sandstone of various 

 types, occurring both in large fragments and in particles of micro- 

 scopic dimensions. Quartz-grains too are very plentiful. In most 

 cases the grit and sandstone-fragments, however small, have well- 

 rounded outlines. The non-igneous material is far more abundant 

 in the coarse ashy conglomerate than in the normal tuffs. The 

 ashy particles, although mainly of types closel}^ resembling the 

 trap or lava of the district, include some which are rather of a 

 trachytic than of an andesitic character. (See PI. XVIII, figs. 5 & 6.) 



1 Quart. Journ. Geol. Soc. vol. lvii (1901) p. 271. 



2 Ibid. vol. lx (1904) p. 154. 



Q. J. G. S. No. 250 ii 



