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This fauna agrees well with 

 that of the Hirnant Lime- 

 stone. Traced in a southerly- 

 direction, this calcareous grit 

 becomes much finer in grain, 

 and flaggy beds are increas- 

 ingly prominent among gritty 

 bands. It seems almost 

 certain that the thick series 

 of fossiliferous flags with 

 some gritty bands exposed at 

 Bryn Dowsi represents ac- 

 tually part of the grit itself 

 as seen below Conway Castle ; 

 and since these beds contain 

 a characteristic Lower Llan- 

 dovery graptolite - fauna, it 

 would appear that the upper 

 part of the grit at any rate 

 (if not the whole) should 

 really be regarded as of 

 Llandovery age. 



(6) Gyffin Shales. 



The Gyffin Shales, which 

 must occupy the bed of the 

 Afon Gyffin for a considerable 

 part of its course, occur in 

 more or less isolated expo- 

 sures, except immediately 

 south of. Conway, since they 

 are only seen in the cores of 

 the folds. With the excep- 

 tion of the lowest members, 

 which are flaggy, the beds 

 consist for the most part of 

 a series of pale-grey pasty 

 mudstones or shales with 

 very thin, soft, black bands 

 containing graptolites ; the 

 beds are always much cleaved, 

 and it is often impossible to 

 obtain recognizable fossils 

 from poor exposures, so that 

 it is not always possible to 

 distinguish between Llando- 

 very and Tarannon rocks. 

 That both series are, how- 

 ever, completely represented 

 becomes perfectly obvious 

 when the fossils obtained 

 from all the different expo- 

 sures are studied together. 



