224 Murchisoris Silurian System. 



Serpuloides (?) longissima, t. vii. fig. 1, and of Crustacea, 

 Homalonotus Jcnightii, (Konig.) t; viii. fig. 9, 10,* and H. 

 Ludensis, Murch. t. viii. fig. 11, Orthocerus Striatum. Some 

 beds contain a small species of Turbo, T. coralii, invested 

 often with a species of coral, Favosites fibrosa, Gold fuss. 

 The third stage of the upper Silurian rocks becomes 

 micaceous, and more argillaceous, occasionally running into 

 large spheroidal concretionary forms ; these beds contain 

 fewer organic remains, but the lowest beds of this division 

 are characterised by a species of Terebratula, T. navicula. 

 t. vii. fig. 16. 



Ludlow or Aymestry Limestone. — The beds just described 

 are occasionally called the mudbeds, from their loose friable 

 structure. They are succeeded by a subcrystalline argilla- 

 ceous blue, or bluish grey limestone of laminated structure, 

 produed by shells and corals. The characteristic fossils of 

 these beds are, Pentameris Knighiii, t. viii. f. i. a. (fig. 1, 

 b. the young.) Lingula Lewisii, t. viii. fig. 4, Terebratula 

 Wilsoni, Bellerophon Aymestriensis, t. viii. fig. 5, Avicula 

 Reticulata, t. viii. fig. 6 ; and corals, Favosites Gothlandica. 

 t. viii. fig. 7, 8, Atrypa Affinis, Terebratula Affinis ; but where 

 the latter become characteristic, Pentamerus Knightii disap- 

 pear. These limestone beds are distinguished by the name 

 of the place where they were first discovered by Mr. Murchi- 

 son, are much less pure than those of the mountain limestone, 

 but their earthy character renders them of great value, as 

 affording a cement which sets in subaqueous operations. 

 Crystals of carbonate of lime and sulphate of barytes are 

 the only minerals observed by Mr. Murchison in this lime- 

 stone. 



* We have selected from the numerous plates in Murchison's work, 

 figures of a few of the most characteristic fossils, of which we have 

 compiled the plates referred to in the text, in order that these remarks, 

 in the absence of the original work, may be more intelligible and useful 

 to observers in India. 



