442 THE LLANDOVERY ROCKS OP MONTGOMERYSHIRE. [Aug. I91I. 







Wenxock. 



List of Wenlock and Ludlow 

 Fossils other than Graptolites. 



Ludlow Shales. 





!=1 . 



d 



1 

 cd 

 cj 



O 



a 



X 



cd 

 « 



X 



3 



pq 







a 













H 

 



1 



X 



X 



X 



J 



u 



H 



X 

 X 



X 



X 

 X 



i . 



" i 

 - i 

 < 



• ■ 

 < 



< ; 



< 

 < 



> 



> 

 > 



< 



< 

 < 



Phacops longicauclatus Murchison 



Ceratiocaris pardoeana La Touche . . . 

 Orthoceras primcevum Salter 



X 



X 



X 

 X 

 X 



* 



X 

 X 



\ 



< 



K 



K 

 K 



Orthoceras subundulatum Portlock 



Orthoceras gregarium Sowerby 



Orthoceras canaliculatum Sowerby ... 

 Orthoceras cf. imbricatum Wahl 





X 



Phragmoceras natitileum Sowerby 



Camarotoechia cf. nucula Sowerby 



Dayia navicula Sowerby 



Leptcena rhomb oidalis Wilck 



Orthis cf. actonice Sowerby 



Pentamerus linguifer Sowerby 



P. (Barrandella) undatus Sowerby ... 



Plectambonites sericea Sowerby 



Phynchonella sp 



Strophomena ci.filosa Sowerby 



Spirifer cf . concinnus Hall 



Wilsonia wilsoni Sowerby 



W. wilsoni, cf. var. sphceroidalis M'Coy 



X 



Pterinea retroflexa Wabl 



Pterinea tenuistriata M'Coy 



Cornularia subtilis Salter 



Ostracoda 



X 

 X 























1 These beds are possibly of Llandovery age. (See p. 438.) 



» VI. Structure of the Area. (Section III, fig. 7, p. 443.) 



The structure of the two valleys dealt with in these pages is by- 

 no means simple. Broadly speaking, the strata are folded into two 

 parallel anticlines with north - north - easterly and south-south- 

 westerly axes, the eastern anticline occupying the Valley of the 

 Severn, and the western the Vale of Guilsfield. Between the two 

 is a crush-zone, consisting of two smaller anticlines crushed against 

 the Bron-y-Buckley Fault, and separated by the Welshpool Dyke. 

 The Welshpool Dyke is probably of the nature of a horst, carrying 

 with it the Trilobite-Dingle Shales, while Silurian strata are let 

 down on either side. 



The Bron-y-Buckley Fault is practically a strike - fault, and 

 so there is but little lateral displacement of the outcrops. The 

 amount of- the_ throw can be surmised by the fact that, at the 

 entrance to Trilobite Dingle, Ludlow Shales are thrown against 

 the Trilobite-Dingle Beds. Since, however, we must allow for the 



