80 



C. MOORE ON ABNORMAL GEOLOGICAL 



operations in the Carboniferous Limestone, it must be manifest that 

 there are a multitude of other examples not yet opened up that 

 would yield an interesting study to the geologist. One of the most 

 difficult problems regarding some of them is to arrive at satisfactory 

 conclusions as to their exact age ; but there can be little doubt 

 that the physical conditions to which the deposits are due were the 

 same both in the Bristol and the Mendip areas. Supposing the 

 fissures in any district had all been caused by the same shrinking or 

 change of level, they would have been subject to the same refilling 

 influences, and would contemporaneously have received a mixture 

 of materials derived from the denudation of that time ; but although 

 the alluvial infillings in the Avenue Quarry have a mixture of 

 organisms, it is a singular fact that in a series of parallel veins 

 coming to the surface on the same horizon, not far removed from 

 one another, and some of them but a few inches in thickness, each 

 appears to have an individuality of its own, and to represent in 

 geological time intervals clearly distinct from one another. As at 

 Holwell, so at Durdham Down, the worked face of the escarpments 

 reveals infillings of alluvium, Oolite, Lias, and Rhastic and Keuper 

 beds, whilst mineralized or iron-ore veins show conditions specially 

 their own. 



Reference has repeatedly been made to the Tubutella ambigua, 

 which I have found in almost every deposit that could be examined 

 under favourable conditions, from Maidenhead to those of Gloucester- 

 shire and Somersetshire. "When they occur, as in the brick-earths 

 of Salisbury, in association with freshwater shells, and also with 

 Postpliocene mammalia, there seems little reason to doubt that 

 they belong to freshwater deposits. If they can be traced in older 

 formations, they may be a guide in determining the conditions under 

 which those formations have been laid down. I have reason to 

 suppose this may be the case between the Upper Devonian and the 

 Carboniferous series. All veins, mineral or otherwise, come to the 

 surface ; and if the Tubutellce be found therein, they will probably 

 indicate the presence of freshwater conditions. The upper portions 

 of those I have mentioned in this district represent the gossans of 

 the lodes in more ancient rocks ; and if, as at Yate and Tytherington, 

 the Tubutella is caught up or surrounded by the mineral matter of 

 the vein, there has either been a remodification of that portion of 

 the vein, or it must have been contemporaneous with the organisms 

 enclosed. 



I have already shown that most of the mineral veins of the 

 Mendips and South Wales are at least of Liassic age ; and on this 

 point I have much confidence in the belief that a careful exami- 

 nation of the gossans and other mineral constituents of the veins in 

 our more ancient rocks will repay the labour, by giving either more 

 precise indications of their age or of the physical conditions under 

 which they were deposited. 



Age of the Bristol Reptilia. — The varied points mentioned in this 

 paper have drawn me away from the chief object which led to their 

 consideration, viz. the age of the Bristol reptilia. As before 



