MONIAN SYSTEM OF ROCKS. 



521 



basal Ordoviclan before reaching Hells Mouth, where only the 

 quartz is left, and the basal Ordovician never appears in the' same 

 form again. The quartz-knob, like others of its kind, dies out on 

 the east side ; and below its expected position are some very 

 Ordovician-looking slates, though not like the black slates of the 

 district nor the grey shales just seen ; and in these there is a lode of 

 copper. 



A little further east rises the greatest quartz-knob of the district, 

 called Craig Wen, and worked for " China stone." This lies, as 

 regards position, above the slates just mentioned, and some red 

 quartz-conglomerates cling closely to its western side. It is imme- 

 diately to the north of this quartz-knob that the ashy slates which 

 have proved fossiliferous occur. We might expect some light to be 

 thrown on the sequence in the cliffs of Borth Wen; but, un- 

 fortunately, both quartz and conglomerate die out before reaching it. 



Fig. 23. — View of Borth Wen, west 



Craig Wen. Fossils. 



1. Quartz. 2.. Eed conglomerate. 3. Fine conglomerate. 



4. Ashes. 6. Slaty ashes. 



What we actually do see is exhibited in fig. 23. On the south side 

 the rocks appear thoroughly confused, masses of quartz roaming 

 about, under no law, among beds of a soft and incoherent character. 

 This might perhaps be attributed to disturbance, but it is much 

 more suggestive of the irregularity caused by the motion and 

 deposit due to siliceous waters, in fact the underground branchings 

 of the quartz-knob. To the north come on, rather rapidly, more 

 regular slaty rocks, of ashy character. I found it impossible to 

 determine the exact way in which these are connected with the 

 disturbed rocks below ; certainly the boundary is not a clean one, and 

 no additional disturbance can be made out. It is in these rocks, at 

 the top of the tramway, that Prof. Hughes has discovered fossils. On 

 the shore, by the pier, stands a mass of quartz, and on its northern 

 side a large mass of coarse red conglomerate. These are followed 

 on the shore by similar ashy shales, and these ashy-looking rocks 

 continue to the end of the cliff, becoming very irregular and losing 

 apparent stratification, and containing several bands of finer and 



