654 



MISS E. M. R. WOOD ON" THE 



[Nov. 1906; 



which we may term the Nant-ysgollon Shales, from a well- 

 known locality at the 

 north-eastern end of the 

 moorland, where these 

 beds are exceptionally well 

 exhibited. They occupy 

 some 350 yards of the 

 river - course, and make 

 their first appearance a 

 few yards to the north of 

 the Ford, where a small 

 tributary stream joins the 

 Tarannon River on its 

 right bank. Here some 

 dark bluish concretionary 

 mudstones and shales, 

 weathering in places to 

 a reddish brown, yield 

 excellent specimens of 

 Cyrt-ograptus MurcJiisoni, 

 Carr., and Monograptus 

 vomerinus, Nich. 



For the next 140 yards 

 sandy flags and shales are 

 exposed at various lo- 

 calities on the right bank 

 of the river. Originally 

 bluish in colour, these 

 rocks weather deeply, and 

 present a dirty greyish- 

 brown or even ashen-grey 

 appearance. They dip at 

 an angle of 35° to 40° 

 north - north - westward. 

 Although no complete 

 specimen of Cyrtograptus 

 Murchisoni has been found 

 in these lower beds, yet 

 isolated branches occur 

 which are almost certainly 

 referable to this species, 



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Eetiolites Geinitzianus, Ban*. (C). 

 Monograptus vomerinus (C). 

 Monograptus crenulatus, Tornq. (f. C). 



Monograptus pi*iodon, Bronn (f. C). 

 Monograptus riccartonensis, Lapw. (R). 



It is difficult in this section, owing to the absence of sufficient 

 exposures,, to fix with exactitude the boundary between the JSTant- 

 ysgollon Shales (Ca) and the overlying Fynyddog Grits (Cb), but 

 the thickness of the shales may be set down at about 450 feet. 



1 In this and succeeding lists of fossils, C = common ; f. C— fairly common ; 

 Bj=rare ; v.R=very rare. 



