DEPOSITS OF NORTH WALES. 361 



About 60 feet below the phosphorite is a bed (see Berwyn section, 

 fig. 2) about 5 feet thick, which is composed chiefly of Orihis sjpiri- 

 feroicles, M'Coy. There are other fossils mixed with this, as Asaphus, 

 Illcenus, Orihis grandis, 0. elegans, 0. expansa, and others ; but 0. 

 spiriferoides is by far the most prevailing form. This same fossilife- 

 rous bed, with its preponderance of Orihis spiriferoides, is found 

 occupying the same position with relation to the phosphorite at 

 Cwmgwynen (see that section, fig. 1) and Llanfyllin ; and from this 

 point it is continued S.E., towards Meifod and Guilsfield, where 

 however the phosphorite bed has not yet been discovered, although, 

 I doubt not, it may be found in its usual position. 



A few yards below the phosphorite bed is another fossiliferous 

 band, in which the most abundant fossil is Orthis Actonice. This 

 is associated with Asaphus (Powisii), Illcenus, Lingula (tenuigra- 

 nulata), together with various species of Orihis and Leptcena. These 

 occur in a very tough limestone, which has, however, sufficient iron 

 in it to decompose where the edge of the bed is exposed to the 

 atmosphere. This bed is very persistent in its character, so much 

 so that I have been able by its appearance on the surface to drive 

 through successfully to the phosphorite beyond. 



Another bed which is continuous over the whole area is that 

 of the " black shales" mixed with sulphate of baryta, which at 

 a distance of from 3 to 5 feet underlies the phosphorite. From 

 its less hardness, it is in the upper surface of this bed that the 

 miners " hole " in working the phosphorite ; so that the whole of 

 the intervening thin limestones have to be taken down. In the 

 year 1870, when on a visit to Penygarnedd, Prof. Morris and myself 

 discovered Graptolites in this bed ; and as soon as the Berwyn mine 

 had been open, I naturally looked for them in the same bed there. 

 There are at the latter place, however, two difficulties in the way 

 of finding the Graptolites. The first is the highly- cleaved nature 

 of the shales ; and the second is the highly pyritized condition of 

 any contained organic remains, so that it is impossible to find 

 Graptolites in their usual form. They are present in abundance, 

 however, as the numerous pyritized stems serve to show. 



The " little limestone," as it is called by the miners, to which 

 I have already referred as immediately underlying the phosphorite, 

 is also a continuous bed. Its upper surface is sometimes covered 

 with minute Brachiopoda and other fossils, among which, at Peny- 

 garnedd, there has been found Calymene brevicapitata. 



Any organic remains which there may ever have been in the 

 phosphorite bed itself have had their structure and form com- 

 pletely destroyed by the chemical changes which have taken place. 

 I have, however, discovered in it what appear to be the remains 

 of Orthoceratites and Lamellibranchiate shells. 



The shales immediately overlying the phosphorite are rich in 

 organic remains. These, when found in proximity to the bed, 

 are all more or less phosphatized. In proportion to the degree in 

 which this has taken place is the degree of the obliteration of the 



