AYMESTRY OR LUDLOW LIMESTONE. 



201 



posing under atmospheric influence, it is well entitled to the name of "mudstone," which 

 in other tracts is applied to large masses of upper Silurian rocks 1 . Like all the mem- 

 bers of the Ludlow formation, these beds are traversed by many joints, more or less 

 vertical, which will be described under a separate head. They are mentioned here to 

 show, that their highly inclined or vertical faces are often marked by lines of small, round, 

 or elliptic cavities (like swallow holes), from three to five inches long, and from one to 

 two inches high. These cavities have clearly once been concretions which ranged 

 along the lines of deposit like the flints in chalk, but in this case, unlike the pure and 

 indestructible flint, the matter of which they have been composed, consisting entirely 

 of a sandy clay, has separated from the harder portions of the rock, and has more easily 

 disintegrated. These beds are less abundantly charged with organic remains than the 

 overlying stages before described, though we meet at intervals with an orthoceratite or 

 one of the above-mentioned characteristic fossils. The lowest stratum, however, of the 

 upper Ludlow is very remarkable, being absolutely loaded with a vast number of small 

 Terebratulse of a gryphoid form, named Terebratula Navicula, PI. 5. fig. 17. This shell 

 is seen in abundance in the escarpments at the View Edge, Mocktree Forest, Downton 

 on the Rock, at various places around the Ludlow promontory, and at Aymestry, always 

 occupying the lowest portion of the Upper Ludlow Rock, and forming the cap of the 

 calcareous zone of Aymestry. In some sections, these terebratulite beds attain a thick- 

 ness of thirty to forty feet. This shell is of great geological value, as we shall see 

 hereafter, being extremely persistent, and marking always the same horizon even to a 

 distance of nearly one hundred miles. The beds which it occupies are sometimes so 

 calcareous, and pass so naturally into the Aymestry limestone, that they may in all such 

 cases be grouped with that rock. 



Aymestry Limestone. — (PL 31, figs. 2, 3, 4 & 5. and c. of wood-cut, p. 196.) 



(See Vignette, chap. 20.) 



The central member of the Ludlow Rocks is a subcrystalline, argillaceous limestone, 

 which might have been termed the Ludlow Limestone ; but as there are few good examples 

 near that town, I have preferred naming it after the beautiful village of Aymestry, where 

 the rock is fully and clearly laid open, and where its fossil contents have been elabo- 

 rately worked out by my friend the Rev. T. T, Lewis 2 . It is there arranged in beds 



' See note, page 204. 



2 The application of his leisure hours to the cultivation of the natural history of his neighbourhood may one 

 day enable Mr. Lewis to confer upon Aymestry the celebrity which White has bequeathed to Selborne. Although 

 this Aymestry limestone is splendidly exhibited in the narrow gorge of the Teme, under Downton on the Rock, 

 in the picturesque demesne of Mr. Thomas Andrew Knight, that place could not have been selected for the name 



