Murchisoris Silurian System. 225 



Lower Ludlow Rock. — Beneath the latter beds, calcareous 

 thin bedded flagstones occur ; the strata seams are formed by 

 thin layers of sandstone; occasionally a substance like fuller's 

 earth occurs between the beds. The colour of the rock in 

 situ is dark grey or black, but it weathers, like all similar 

 beds of the upper Silurian system, to light ashen grey. 

 These beds are distinguished by many peculiar organic 

 remains, which have not been observed in any overlying 

 stratum, viz. Cardiola interrupted, Phragmoceras Nautileum, 

 t. viii. fig. 12, 13, Orthocerus filosum, O. Pyriforme, 

 t. viii. fig. 2, Lituites giganteus, together with Trilobites, 

 as Calymene Blumenbachii and Asaphus caudatus, but 

 these last fossils are equally found in the subjacent beds. 

 With the exception of thin seams of galena, and a little 

 iron pyrites, no minerals have been found in this rock. The 

 entire thickness of the Ludlow rocks is estimated by Mr. 

 Murchison at 1,500 feet. 



Wenlock Limestone, or Ballstone. The next member of 

 the Silurian system corresponds with a limestone which pro- 

 jects abruptly through the coal formation at Dudley, where 

 the intermediate beds being wanting, it was impossible to as- 

 certain its place in the geological series. This limestone 

 is distinguished by its containing masses of a crystalline 

 limestone, highly charged with corals and encrinites, so much 

 so, as to be liable to be mistaken for mountain limestone ; but 

 on further enquiry, it is found, that the crenoidal remains 

 contained in this rock are peculiar to itself, or at least dis- 

 tinct from those of the mountain limestone. The ordinary 

 colour of the rock is dark grey, freckled with veins and 

 strings of white carbonate of lime. The beds are broken and 

 irregular, with deposits of shale contained in the crevices. 

 This last is so abundant, as to give the limestone an earthy 

 appearance, and to constitute one of the best characters of 

 the rock. In other cases, all traces of bedding are wanting, 

 and the whole calcareous mass is made up of concretions 



