238 PROF. S. H. REYNOLDS OX A SILURIAN [May 1907, 



V. Summary and Conclusions. 



It is claimed that this paper establishes the following points :— 



1. That the trap-rocks of the Eastern Mendips are not intrusions 

 in the Old Red Sandstone, but contemporaneous flows associated 

 with an underlying series of normal tuffs, and with a mass of coarse 

 ashy conglomerate which probably forms two necks marking the 

 source whence the other igneous matter was ejected. 



2. That the finer tuffs contain a considerable series of fossils of 

 (probably) Upper Llandovery age, proving that the whole volcanic 

 episode took place in Silurian times. The area is therefore closely 

 comparable to that of Tortworth, and constitutes a second district in 

 Great Britain in which volcanic rocks of Silurian age are known to 

 occur. The occurrence is established of an additional inlier of 

 Silurian rocks at a distance some 30 miles farther south than they 

 had been previously recognized in the West of England. 



3. The andesitic character of the lavas is confirmed. 



EXPLANATION OF PLATE XVIII. 



Fig. 1. Pyroxene-andesite, Moon's Hill. — The section shows parts 

 of a well-formed bastite-pseudomorph after enstatite, and of a broken 

 augite-crystal. X about 12. See p. 230. 



2. Pyroxene-andesite, Sunnyhill. — On the right is a weathered 



plagioclase-crystal, on the left are several bastite-pseudomorphs after 

 enstatite ; round these the groundmass, which contains much ferric 

 oxide, shows fluxion-structure. X about 12. See p. 231. 



3. Tuff-band No. 3, Sunnyhill. — The rock consists mainly of andesitic 



fragments of several types, mingled with a certain number of broken 

 felspar-crystals. These are all closely packed together, and in some 

 cases the fragments are much stained with ferric oxide. X about 12. 

 See p. 233. 



4. Fossiliferou s felspathic tuff, south-west of Tadhill 



Farm. — The section shows broken felspar-erystals, and andesitic 

 fragments, which are often converted into a yellow palagonitic 

 substance, mingled together in fairly-equal proportions. X about 15. 

 See p. 233. 



5. Matrix of the coarse ashy conglomerate, New Quarry 



south-east of Moon's Hill. — The section shows (1) numerous 

 quartz-grains, (2) well-rounded and subangular pieces of grit, (3) ashy 

 fragments of more than one type. X about 15. See p. 233. 



6. Matrix of the coarse ashy conglomerate, Butts, Beacon 



Hill. — The rock is mainly composed of small andesitic fragments 

 often strongly iron-stained, and showing very irregular outlines. 

 Some felspar-crystals and quartz-grains are also present. X about 15. 

 See p. 233. 



Discussion. 



The Chairman (Dr. A. Strahan) remarked that this paper showed 

 how much might remain to be learnt in districts which appeared to 

 be well known. He had himself crossed the region a few years ago, 

 and had seen no reason to suspect the existence of a Silurian inlier. 

 Since then a number of sections had been opened ; and, in a recent 

 visit to them and to the various trenches opened by the Author, 

 he had been impressed with the conclusive character of the evidence 

 brought forward. To what precise part of the Silurian system the 

 fossiliferous ashes should be referred was a minor point ; the chief 

 interest lay in the existence of the inlier and in the determination 

 of the Silurian age of the volcanic group. The ' ashy conglomerate,' 



