SILURIAN SYSTEM—WENLOCK LIMESTONE.

455

or Upper Ludlow rock, being flanked by greenish micaceous tilestone and red marl of the Old RedSandstone, and also by very hard greenish grit of the same formation. These beds are more orless coated with red oxide of iron. They are much jointed; the dominant joints ranging fromS.S.E. to N.N.W. are traversed by others, occasioning these flaglike strata to split into a numberof dice-shaped and rhombic forms.

With the exception of these beds at Purton, the only other evidence of the existence of what maybe termed Ludlow rock, is at the Horse-shoe farm, below the north-eastern end of Milbury Heath,and consequently at the other extremity of the district. A few beds there contain some of thefossils, particularly Cypricardia amygdalina, and pass conformably into the overlying Old RedSandstone, and downwards into beds with ylsuphus caudatus, &c. After all, this Silurian forma-tion is so very feebly exhibited in the Tortworth tract, and offers such slight lithological analogiesto the best types, that without a long acquaintance with it in other districts, its recognition wouldbe impracticable.

Wenlock Limestone.

The Ludlow rock, at Purton, is underlaid by calcareous beds containing masses of corals and shells,among the latter of which is the Productus depressus together with many Orthocerata. From thefossils I conclude, that these beds represent the Wenlock limestone, of the existence of which thereis abundant evidence in the south-western branch of the Silurian fork, which clasps round theOld Red Sandstone of Tortworth. Thus, we see this limestone commencing at Skeays Grove,near Falfield Green (quarries long abandoned), whence it extends in a separate narrow ridge byFalfield Mill to Brinmarsh, and afterwards sweeps round in a low, circular, dome-like form toWhitfield, where it dips outwards, passing on all sides under the overlying formations. For ashort distance, near Falfield, this ridge is double, the upper portion being seen in Barber’s quarry.The best section of the Wenlock limestone, particularly the lower part, is at Falfield windmill,where it is made up of the following beds in descending order:

1. Rubbly red, sandy, calcareous beds.

2. Thin, irregularly bedded, almost lenticular masses of purple and grey limestone, passing down into ash-coloured shale,with very thin courses of greyish blue limestone, the shale being loaded with many of the corals and encrinites peculiar tothe Wenlock limestone, and small mollusks, such as the small Spirifer radiatus, of Dudley; the Orthis canalis, so commonat Woolhope and many other places.

3. Purple and grey strong-bedded limestone, 20 to 30 feet thick, highly charged with encrinites, and the beds separatedby courses of red shale.

4. Red and green schistose beds passing down into hard purple sandstone and grit.

The beds dip 45° to the east. They present in their red colour and general aspect, as well as in their fossils, a strikinganalogy to other beds of this age at Clencher’s Mill, near Ledbury, p. 413. Dr. Cooke and Mr. Weaver have further col-lected in them the Calymene Blumenbachii, Asaphus caudatus, and other fossils.

At Whitfield quarries, where the same calcareous beds rise in a low dome, there are also manyfossils. In the upper part, the rock consists of irregular concretions of impure grey limestone,with purple and whitish green marls, passing down into finely laminated, ashen-green and deep-redslaty marl, with irregular thin courses and concretions of strontian; next, flaglike sandstone, in bedsof two to three inches. The lowest part consists of thick-bedded encrinite limestone, of purple andgrey colours, containing corals and shells and passing down into slaty shale, &c. These calcareousbeds are here about 15 feet thick, and uniformly rest upon the sandstone and shale of the Caradocformation.

3 L 2