120 ME. H. LAPWOETH ON THE [Feb. I9OO, 



fossils. They are, however, highly cleaved ; fragments only of 

 graptolites may be extracted, and these with difficulty. From a few 

 blue bands about 100 yards above the lane the following forms 

 have been obtained : — Monograptus turriculatus, Barr., M. Becki, 

 Barr., M. Sedgwickii-tj^e, M.jaculum, Lapw. and Eastrites distorts, 

 Lapw. Orange-coloured worm-trails are of frequent occurrence 

 throughout the group. The general dip is from 10° to 15° down- 

 stream. 



As we leave the brook and ascend the steeps of the Gyrn escarp- 

 ment, the rock is seen to become more highly cleaved, and of shaly 

 rather than a mudstone type. At the same time a variable dip 

 sets in, and at the summit folding and even inversion seems to have 

 taken place. Graptolites are rare, and can only be seen on the 

 sharp edges of the shales. One orange-weathering band about half- 

 way up the slope contains Monograptus lobiferus, M. BecH-type, 

 M. ruucinatus, Lapw. and M. jaculum. 



Excellent exposures of these pale shales are visible in the new 

 road-diversions at Llanfadog-Isaf, in the sides of the railway-cutting, 

 and in the banks of the Elan close to the small footbridge at Coed-y- 

 mynach. They are crammed, as a rule, with orange-coloured 

 worm-markings, and dip uniformly at from 10° to 15° southward 

 and south-eastward. From the new road-cuttings I have extracted 

 Monograptus runcinatus and M. Becli. 



A very fossiliferous set of rocks at the base of the Rhayader 

 Group has been opened out in the side of the Cambrian Itailway- 

 cuttings, a short distance north of the level crossing at Glan Elan. 

 The rock is a pale bluish- grey mudstone. Seams of orange 

 limonito yield graptolites, preserved in the same material. These 

 include Monograptus Sedgwickii, M. crassus, Lapw., M. lobiferus 

 var. undidatus, Perner, and Petalogroptus palmeus var. tenuis, 

 Barr. Farther north along the line, on either side of the tunnel, 

 the cuttings have exposed fine sections of these shales. They are, 

 however, barren of fossils. 



In the Wye Yalley, at the bend south of St. Winifred's Church, 

 a series of purple mudstones, intermingled with pale green mud- 

 stones, come in. Their chief interest consists in their purely 

 local occurrence. The cuttings for the Birmingham Aqueduct 

 exhibited a complete section of these bands in the sides of the 

 trench, but in no other locality does there appear to be the least 

 sign of this remarkable set of purple rocks. It is to be regretted, 

 lor they form bands so distinct that the process of following 

 them out in the field would have been simple, and at the same 

 time would have enabled us to form some idea of the structure of 

 these basement-beds. 



The junction of the Rhayader and Gwastaden Groups was not 

 revealed in the trench, the rocks being covered by a thick mass 

 of Drift. This again was especially unfortunate, for it would 

 have been very interesting to have actually seen the one group 

 resting unconformably upon the other. 



