Vol. 56.] 



SHALES OF THE WELSH BORDERLAND. 



38 L 



There is an almost continuous section exposed on one bank or the 

 other, from immediately above the suspension-bridge to beyond Wern 

 Wood ; but the exposures in the upper parts of the course of the 

 river are merely repetitions of beds seen lower down, and therefore 

 the most important part is that seen between the suspension-bridge 

 and the high cliff just beyond the weir. This affords a section 

 from beds of undoubted Wenlock-Shale age into a set of beds whose 

 fauna proclaims them to belong to the Lower Ludlow. 



There are no rock-exposures between the mouth of the Irfon and 

 the suspension-bridge ; but between that bridge and Park Farm 

 several rock-exposures were visible in the summer of 1898, though 

 they must, as a general rule, be covered by the water : these are 

 all on the left bank. The beds strike N. 30° E., and dip in towards 

 the river at an angle of 25° ; they consist of a series of hard calca- 

 reous shales, overlain by a softer shale-series. Fossils are abun- 

 dant, and include those enumerated in Table II, col. A (p. 384). 

 These beds undoubtedly represent the zone of Cyrtograptus rigidus. 



The next beds in ascending order are seen on the right bank of 

 the river ; they are exposed from a point opposite where the road 

 curves away from the farm on the left bank till where the convex 

 curve of the right bank begins. These beds consist for the most 

 part of hard calcareous flags with large limestone-concretions, some 

 of which measure as much as 3| feet in transverse diameter. 

 Graptolites are fairly abundant in the 

 more shaly bands, which are seen be- 

 tween the flagstones. The graptolites col- 

 lected from this horizon are enumerated in 

 Table II, cols. B & C (p. 384). In addition 

 Cardiola interrwpta, Phacops Musheni, 

 Salt. ?, and Orthoceras sp. occur. These 

 beds certainly, then, belong to the C- 

 Lundgreni zone. 



Fig. 1. — Map. 



^Lower 

 WLudlow 



Section exposed 

 al ong the R. Ir fon 



Scale O mi 



There is a conspicuous change in the strike of the beds at this 

 locality from that seen in the beds near Park F'arm, and the dip is 

 also changed in amount. These beds strike E. 10° N., and dip up 

 the river at an angle of 10°, This variation seems to indicate that 

 the succession is not perfectly normal ; in fact, the evidence seems 



Q.J. G.S. No. 222. 2d 



