Vol. 56.] 



SILURIAN SEQUENCE OF RHAYADER. 



85 



of the Gwastaden Group are no longer visible. The Ehayader 

 Pale Shales, however, are well shown in the Mid Wales Railway- 

 tunnel : but they are barren of fossils. 



It will be seen that in this second line of traverse, with the 

 exception of the break in the river-valley, the sequence of the beds 

 corresponds well with that obtained in our first section. 



The 



Fig. 2. — Section through Woodlands from Gwastaden Cairn to the 

 Cambrian Railway-line. 



MW, 



if 



Gwastaden 



S.£. 



[Approximate length = 1£ miles.] 



Pig. 3. — Section from Gwastaden to Rhyd-hir Brook. 



Ac, 



[Approximate length = 1 mile.] 



6'= Rhayader Pale Shales. 

 A = Gwastaden Group. 

 JcZ=Gigrin Mudstones. 



Ad 2 — Zon.Q of M. conoolutus. 

 Ad x = Calcareous-Nodule Beds. 

 Ac=~Ddo\ Shales. 



Ac 3 = Zone of M. fimbriatus. 



Ab=T>j&cyn Flags. 



Ab 3 =D.-modestus Flags. 



y^> 2 =E,ottenstone Beds. 



Ab x = Micaceous Flags and Grits. 

 ^4a = Gerig Gwynion Grits. 



x= Blue-black Shales. 

 //= Faults. 



greater part of the Ddol Shales, and the whole of the Biplo- 

 graptus-rnodestus Flags, however, are missing, being apparently 

 covered by the river- alluvium ; moreover, only a fraction of the 

 Gigrin Mudstone division (Ad) is displayed. A good part of 

 these missing beds is exhibited in the section (fig. 3, above) described 

 on the following page. 



