part 3] siluriax rocks of the clux-forest district. 233 



the neighbourhood of Bucknell itself. The greenish Upper Cho- 

 netes Beds again pass gradually into dark, brittle, thinly-laminated 

 shales. At various horizons, and in some places throughout their 

 entire thickness, these shales have a very curious structure. When 

 broken into slabs they present a puckered appearance, like ripple- 

 marking on a small scale, with the crests of the ' ripples * about 

 half an inch apart and much broken up. These beds are more 

 resistant to weathering than lower beds, and hence are often seen as 

 relict blocks in the fields. The fossil-content of these shales varies 

 greatly both horizontally and vertically. In the lower part, where 

 the bedding is more regular, Lingula minima frequently occurs. 

 Platyscliisma lieUcites is found throughout the shales, and is 

 often so abundant as to form bands of hard compact limestone 

 weathering to a soft brownish rock. 2Io<liolop$is complanata is 

 frequently associated with Platysehisma. In the upper part of 

 the shales, where the puckered structure is usually well developed, 

 fossils are comparatively rare and are always distorted. The 

 distortion is principally in a vertical direction, and the fossils are so 

 pressed down into the matrix that they present very indistinct 

 outlines. Platyschisma J/elicites and a species of HolnpeUa are 

 the types that most frequently show this crushing. 



Some species from the Chonetes Beds survive into these shales, 

 and Rhynclionella nucula, Chonetes sfriatella, and Orthis lunata 

 arc occasionally found associated with the typical fossil Platy- 

 seliisma helicites. 



The occurrence of Platyschisma and Holopella throughout these 

 beds is a point of great interest, since, in the Ludlow district, the 

 former fossil is limited to one thin band. 



Bands of sandstone make their appearance in the upper part 

 of the shales (typical sections will be described in detail later), and 

 the latter are succeeded finally by a hard bedded sandstone of a 

 greenish colour, which, after 12 or 18 inches, becomes yellow and 

 massive and similar to the typical Downton Sandstone of the 

 Ludlow area. The yellow sandstone is about 5 or 6 feet thick, 

 and passes upwards into yellow, thinly-bedded, micaceous tile- 

 stones. The tilestones are about a foot thick, and are succeeded 

 by more rudely-bedded green micaceous sandstones, followed by 

 green marl with one or two hard grit-bands of a similar colour. It 

 is evident that the limit of the Downton Sandstone is formed by 

 the yellow tilestones. 



The smaller outlier (Five Turnings Outlier) is marked 'tilestones ' 

 on the Geological Survey map, 1 and the beds were therefore in- 

 cluded by the Surveyors in the Old Red Sandstone Series. Similar 

 beds in the larger outlier (Clun Outlier) are not indicated, but the 

 base of the so-called Old Red Sandstone is designated ' Green Marl.' 

 The shales, which underlie the tilestones and have been shown 

 to belong to the Downton-Castle Sandstone Series, were classed as 

 the highest beds of the Upper Ludlow Series. 



1 One-inch. Old Series. 53 X.E, 



