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SILURIAN SYSTEM — CARADOC SANDSTONE. 



Caradoc Sandstone» 



The Caradoc sandstone forms the great mass of the Silurian rocks of the Tort worth 

 tract ; for while the overlying formations are miniature representatives of their types in 

 other parts, the lower sandstone, associated with much red shale, covers an extensive 

 area. Rising from beneath the upper strata at Purton, it first occupies a ridge in 

 Scotts Hill, and advancing towards Tortworth, expands over the flat denudations of 

 Halmore and Breadstone Green, and passing to the east of Berkeley, in unconformable 

 juxtaposition to the Old Red Sandstone, occupies an area about three miles in width at 

 Woodford Hill, Stone and Michaelwood Chace, whence the formation is projected to the 

 S.S.E. and S.S.W. in two narrow bands, the eastern of which supports the limestone 

 of Fahield and Whitfield. In many parts of this district the sandstone is so subordi- 

 nate to the shale, that the deposit is familiarly known among the country people 

 as "the clays," and where these abound, and the surface has been much denuded, as 

 is the case at Berkeley Heath and Halmore Green, it is difficult to define the subsoil 

 of Silurian rock, from that of the Old Red Sandstone or even of the lias. There are, 

 however, certain helps by which the place of the Silurian Rock can be ascertained ; 

 such as the occasional sinking of a well, and by the deep ruts bringing up to the sur- 

 face fragments of the thinly laminated beds, usually containing casts of characteristic 

 fossils. To an eye practised in the district, the mere lithological structure of these 

 beds is very dissimilar from that of any of the surrounding and overlying formations ; 

 the minuteness of the grains, the fine dissemination and intimate admixture of very 

 small scales of mica, being alone sufficient to mark them. There are, besides, many 

 clear sections of this formation, on the southern edge of Michaelwood Chace, on both 

 banks of the Avon near Damory Mill, and at Stone ; particularly on the sides of the 

 Bristol road, near the Fox public-house. The sandstone and associated shale seem to 

 contain a large portion of the oxide of iron, and consequently are as red in colour as 

 any of the overlying groups. In colour, indeed, they present an exact parallel to many 

 masses of the Caradoc sandstone of Salop, and are also perfectly un distinguish able 

 from those of May Hill, many portions of which might (in the absence of shells) be 

 mistaken for either New or Old Red Sandstone. The sandstone is sometimes very 

 compact, and the beds vary in thickness from two to ten inches, whilst the shale is 

 constantly in that state which by most observers would be termed slate marl. There 

 is one thick bed of hard grit, used as building-stone in Michaelwood Chace. 



The strata are inclined at all angles and in various directions, but generally they dip 

 beneath the overlying formations south of Tortworth. The exceptions are found near 

 masses of trap rock or along lines of fracture west of Stone, where beds of this age are 

 thrown into unconformable contact with the Old Red Sandstone, dipping 70° west ; or 

 again near Falfield where they are raised from beneath the limestone in domes or arches, 



