Yol. 65.] OKDOVICIAN AND SILTTKIAN ROCKS OP CONWAY. 181 



At Locality 7 : 



Dicranograptus brevicaulis, E f & W. ! Climacograptus bicornis, Hall. 



(abundant). I Climacograptus antiquus, var. litieatus, 

 Mesograptus multidens, E. & W. E. & W. 



(abundant), and var. compactus, • Climacograptus scharenbergi, Lapw. 



E. & W. I Thysanograptus harknessi (Lapw.). 



At Locality 6 : 



Dicranograptus brevicaulis, E. & W. I Thysanograptus harknessi (Lapw.). 

 "—graptus multidens, E. & W. 



At Locality 5 Orthograptus calcaratus var. vulgatus, E. & Yf., is 

 abundant, with rarer Dicranograptus brevicaulis and Mesograptus 

 multidens. 



All these flags and shales, including localities 9-5, may be 

 termed the Zone of Mesograptus multidens and Dicrano- 

 graptus brevicaulis, since both these fossils are characteristic 

 forms throughout. 



Black 'blocky' shales then succeed, the fauna of which differs 

 from that just described, mainly in the abundance of Orthograptus 

 truncatus var. intermedins, E. & W. Other common graptolites are 

 Orthograptus vulgatus, E. & W., Olyptograptus euglyphus (Lapw.), 

 and Climacograptus scharenbergi, Lapw. These beds are fairly 

 thick ; but, towards the end of the section, they give place to soft 

 black shivery shales (weathering orange), which contain a very 

 different fauna, namely : — 



At Locality 3 : 



Abundant Orthograptus truncatus (Lapw.). 



And at Locality 2 : 



Climacograptus minimus, Carr. 



Dicranograptus nicholsoni, Hopk. 

 Dicranograptus ramosus, Hall. 

 Climacograptus bicornis, Hall. 



Orthograptus truncatus (Lapw.). 



The incoming of Orthograptus truncatus is characteristic of the 

 Zone of Dicranograptus clingani, and the other graptolites are all 

 forms commonly associated with it. It seems, therefore, fairly 

 clear that these beds represent that horizon, while the black 

 blocky shales immediately below must, I think, represent the 

 Zone of Climacograptus wilsoni, which is commonly characterized 

 by the presence of Orthograptus truncatus var. intermedius, here 

 the most abundant species. 



These shivery shales are at once succeeded, without any break, 

 by the Bodeidda Mudstones, with their characteristic Trinucleus- 

 fauna; from Locality 1, in addition to remains of Trinucleus, there 

 w r as obtained the tail of a large Asaphid (possibly Asaphus radiatus 

 or A. nobilis). 



These same black Dicranograptus-Shales are also seen east of the 

 river, in a much attenuated form. At the base there, they have a 

 distinct limestone-band, full of the remains of large brachiopoda ; 



