228 PROCEEDINGS COTTESWOLD CLUB 1909 
The portion of the Mendip Hills visited is of anticlinal structure. 
In the centre, and revealed by denudation, are Silurian rocks (pro- 
bably of Upper-Llandovery age) with contemporaneous volcanic rocks 
that comprise beds of volcanic tuff, ashy conglomerate and pyroxene- 
andesite. The pyroxene-andesites are the old lava-flows; the volcanic 
tuffs, the fragments of lava, etc., which were ejected from the volcanoes 
and fell into the sea, becoming associated with the mud there accumulat- 
ing ; while the ashy conglomerates may be either what are technically 
known as ‘‘ volcanic conglomerates,” or the constituent masses may 
have been rounded by hurtling against each other in the vents and there- 
fore in practically their actual position. All this volcanic activity took 
place before the Old Red Sandstone was deposited, and was probably 
contemporaneous with that at Tortworth. Tortworth was the first 
place in England where volcanic rocks of Silurian age were found, 
and this locality and the Mendip Hills are the only two where the 
phenomena may be studied. The succeeding Old-Red beds in the 
Mendip Hills are comparatively thin, and between them and the 
underlying Silurians is a non-sequence, for there are no indications 
of the Temeside or Ludlow rocks, nor of the Wenlock, for the Mendip 
Silurians are most likely Upper Llandovery. The Old Red Sand- 
stone closely flanks the Silurian rocks and gives rise to some of the 
loftiest and most barren ground in the Mendips. To the Old Red 
succeeds the Lower Limestone Shales, and to these the Carboniferous 
Limestone, which is extensively worked at the Waterlip Quarry. 
Along the south side of this portion of the Mendip Hills the Lower 
Limestone Shales and Carboniferous Limestone have not uninterrupted 
outcrops, for the Lias and Oolite oversteps them in places, coming 
into direct contact with the Old Red Sandstone. But on the northern 
side Lower Limestone Shales, Carboniferous Limestone, Millstone- 
Grit, and Coal-Measures succeed one another, and have continuous 
outcrops, although in places the strata are much faulted. Here and 
there are outlying patches of ‘‘ Dolomitic Conglomerate ” (Keuper) 
and Lower Lias resting directly and non-sequentially upon the 
Paleozoic rocks. 
The party were fortunate in having with them Prof. S. H. 
Reynolds, who was the first to discover Silurian rocks in the Mendip 
Hills, and to establish the contemporancity with them of the igneous 
rocks.*. Before, the igneous rocks—which were first discovered by 
the most indefatigable of Somerset geologists, and one. who has done 
yeoman work, namely Charles Moore—were thought to be intrusive 
in the Old Red Sandstone, and to have been the prime factor in 
elevating the Mendip Hills. These hills have ever been a line of 
weakness, and movements along their axis have been repeated in 
Paleozoic and Neozoic times. During the greater part of the Triassic 
Period and the earlier half of the Jurassic, they were certainly dry 
ground. The ‘‘ Dolomitic Conglomerate” occupies hollows in the 
Limestone or Old Red as the case may be, and although many 
x Quart. Journ. Geol. Soc., vol. Ixiii (1907), pp. 217-238. 
