70 



there worked, occur several beds of tuff, or volcanic ash which has 

 by age, pressure, and possibly heat, been solidified into hard rock. 

 Novv', although fossils are naturally never found in volcanic lavas, 

 they are occasionally found in volcanic ashes or tuff. Fossils can 

 only be preserved in beds of this nature when the ashes, having 

 originally fallen on the surface of the sea or of lakes, and sunk 

 gradually to the bottom, have enveloped and killed any organisms 

 that were living there at the time, these usually being mollusca, 

 crustaceans, and more rarely sea plants. It occurred then to Prof. 

 Reynolds to carefully examine these beds of tuff, and his search at 

 one spot near the entrance to the quarry where the tuff was softer 

 and more fragile, was rewarded by the discovery of certain shells 

 and crustacean remains, which instead of being of Old Red Sandstone 

 age, proved to be undoubted Silurian fossils. 



Here then was a great discovery. If this were so, it was 

 evident that the tuff or ash had been thrown up and had descended 

 from a volcano during the Silurian period, and long before the Old 

 Red Sandstone rocks had been laid down. Moreover, the igneous or 

 trap rock in which the beds of tuff occurred must also be of the same 

 age, and hence it seemed probable that Silurian strata — which had 

 been formed about the time during which volcanic action was pro- 

 ceeding — would be found close to the position of the eruptive rocks. 

 A very careful search was therefore made in the immediate neigh- 

 bourhood. On the other side of the road, a few hundred yards 

 distant irom Sunnyhill is Moon's Hill Quarry, which has been worked 

 for many years for road metal, but from the Audesite or trap rock 

 quarried there nothing could be learnt. Unfortunately there were 

 no other exposures of strata in the neighbourhood, and it was 

 very difficult to obtain evidence of the extent of the trap, although 

 from the constant occurrence of fragments in hedgebanks and in the 

 fields it seemed probable that the area covered was very considerable. 

 If the edge of the mass of trap could be found and an exposure 

 made shewing the strata it rested upon, this would probably be 

 found to be of Silurian age. Some help was obtained from frag- 

 ments of stone thrown out from rabbit and mole holes in the fields, 

 and in one spot, 300 yards south-south-west of Tadhill Farm, Prof. 

 Reynolds found tuff with Silurian fossils. 



The area between Tadhill Farm and Moon's Hill Quarry is 

 occupied by a mass of coarse ashy conglomerate, which was 

 exposed in 1905 in a temporary quarry between Moon's Hill and a 

 farm a short distance off. This curious conglomerate consists, 

 according to Prof. Reynolds, of a fine-grained ashy matrix similar 

 to that of the normal tuff of the district, embedding blocks and 

 pieces of rock, some as large as 18 inches in diameter, mostly of the 

 local trap rock, and thoroughly well rounded, although a few of the 

 larger are sub-angular, or only partially rounded. No fossils were 

 found in this exposure, but the possible origin of this rock will be 

 referred to later. 



Since, however, Prof. Reynolds published his results in a paper 

 entitled " A Silurian Inlier in the Eastern Mendips," in the Quarterly 



