GEOLOGY OF THE BRISTOL COALFIELD. 39 



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BY W. W. STODDART, F.C.S., F.G.S., &c. 



PART 5.-THE TRIAS8IC PERIOD. 



A COMPARATIVE calmness in the deposition of strata 

 followed the close of the Coal measures, the large and 

 important accumulations of vegetable remains being covered up 

 and buried beneath the sands and fragments of rocks broken and 

 washed up by the waters of a shallow sea. The wear and tear of 

 the rocky shore by water and atmospheric forces were extremely 

 great, and the clehris were distributed far and wide over the surface 

 of the country, filling up every cavity and depression, so that the 

 Carboniferous forests were b uried beneath a solid roof of boulders 

 and fragments of rock. These boulders and fragments were in 

 the course of time cemented together by the infiltration of lime 

 and magnesia, hermetically sealed from atmospheric influences. 

 This may now be seen over the Severn tunnel, and so regularly is 

 this the case with the upper coal beds that the colliers of 

 Gloucestershire and Somersetshire have given it the provincial 

 name of "overlie." Thus was formed what we now know as 

 the Dolomitic conglomerate. This conglomerate is always found 

 composed of fragments of the adjacent hills and firmly fastened 



