362 D. C. DAV1ES ON THE PHOSPHOKITE 



marks and original form of the fossil. At the Berwyn mine this 

 process of phosphatization is most complete. At Llan-y-mowddwy, 

 where sulphur largely takes the place of phosphate of lime, the 

 nodules, which are there plentiful in the shales, are all oxidized. 



At Cwmgwynen (see section, fig. 1) the approach to the phosphorite 

 is from the upper side, consequently a good series of these overlying 

 shales is traversed. It is there seen that as the distance is increased 

 from the hed itself the fossils lose their phosphatic character. I 

 have collected from these beds at Cwmgwynen Echinosphcerites 

 (balticus), Garyocystites, and other Echinoderms, Lingulce, Modiolce, 

 Theca Forbesii, Oycloceras arcuatum, and C. sonaoc, Orthocerata. 

 Illcenus Davisii, and other fossils. 



It will be seen by a reference to the sections that strata in which 

 the deposit occurs are, throughout the region described, highly in- 

 clined, perpendicular, reversed, and contorted. On the whole, this 

 nearly vertical condition of the strata is favourable to the processes 

 of mining. 



By a reference to the analyses which I append to this paper, it 

 will be seen that the composition of the bed is very uniform over a 

 large area, the picked samples at Cwmgwynen and Berwyn mines, 

 yielding over 60 per cent., and the bulk of the beds, both at these 

 places and at Penygarnedd, making 46 per cent, of phosphate of 

 lime. In the neighbourhood of Llanfyllin, however, where the sub- 

 jacent limestone becomes more arenaceous in its nature, the quantity 

 of phosphate dwindles down, as at Green Park, to 20 per cent. An 

 important change has also taken place in the composition of the 

 bed before it emerges from under the Berwyn mountains, in its 

 western outcrop, on the flanks of Aran Mowddwy. There sulphur 

 has taken the place of the phosphate of lime, which is reduced to a 

 minimum. I may here remark in passing, that the phosphorite bed 

 has yet to be searched for, north of this point, along the western 

 outcrop of the Bala Limestone, towards Bala. 



In attempting to account for the existence of this bed, we cannot 

 be far wrong, I think, in ascribing to it an organic origin. It is in 

 all probability an old sea-bottom, on which the phosphatic matter of 

 Crustacean and Molluscan life was precipitated and stored during a 

 long period. Certain marine plants may also have contributed their 

 mite of phosphatic matter; but the quantity furnished by them 

 would, I think, be small. It is possible also that a great abundance 

 of marine vegetation, taken with a deficiency of Crustacean and 

 Molluscan life, may partly account for the altered character of the 

 bed on its western outcrop. The abundance of vegetable which was 

 evidently mixed up with the animal organisms of the period is 

 evidenced by the quantity of graphite and sulphur which everywhere 

 are present in the phosphorite bed. 



I see no reason to alter the opinion expressed by me in the year 

 1867, in the communication to the ' Geological Magazine ' already 

 referred to, as follows : — " We may, I think, regard the phosphate 

 bed as the remains of a laminarian zone of sea-life, just as the wide- 

 stretching ferruginous sandy layers in the same formation, with their 



