Hughes — Silurian Bocks of Casterton Low Fell. 207 





variations all along the ridge. . 

 In the lowest beds Gro.pto- 

 lites, probably G. priodon, and 

 an Orfhoceras, like 0. tenui- 

 cinctum, ocGuv. Further North 

 we find these flaggy beds suc- 

 ceeded by alternations of a 

 coarse greywacke,'with joints 

 at right angles to the bed- 

 ding and a roughly cleaved, 

 distinctly bedded sandstone. 

 All this part of the series I 

 have included under (a), and 

 would estimate its thickness 

 at about 1000 feet. 



It it succeeded by about 

 1200 feet of unfossiliferous 

 greywacke (&), with occa- 

 sional bands of red earthy 

 nodules in the upper part, 

 and alternations of finer 

 sandstone sometimes roughly 

 cleaved. 



These are succeeded by a 

 set of dark grey shivery sand- 

 stones (c), (d) and (e), about 

 3000 feet thick, with occa- 

 sional beds of tough grey- 

 wacke and generally a rough 

 cleavage in the softer beds. 

 Gardiola interrupta occurs all 

 through (c) and (d), but the 

 specimens are not so fine or 

 so numerous in the middle 

 part (c?) as in the lower (c). 

 I procured many fine ones 

 from the Fell Eoad side near 

 where it crosses Filer Beck. 

 In the middle part (d) a very 

 interesting set of fossils oc- 

 curs, among which the fol- 

 lowing have been determined 

 by my colleague, Mr. Ethe- 

 ridge : — 



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' I use the word greywacke 

 merely as a lithological term for 

 the rough, tough, gritty sandstones, 

 BO common in the Palseozoic rocks ; 

 the term grit being required fox the 



coarse-grained rock intermediate between sandstone aijd conglomerate, e.g. Millstone 

 grit. * 



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