226 Murchisoris Silurian System. 



feet. The limestone is of a dark grey or black colour, in 

 which, as well as in the absence of a concretionary structure, 

 it is quite unlike the Wenlock limestone of the old Silurian 

 system. 



It would be extremely important indeed if we could es- 

 tablish good distinguishing characters between the limestone 

 of the coal measures and that of the more ancient formations, 

 but this, if a matter of difficulty in England, is at least an 

 equally difficult thing in India. It is true the subject has here 

 been as yet little investigated, but we cannot place the least 

 confidence in those practical men who employ names with- 

 out thinking of their meaning, and speak confidently of lias, 

 and carboniferous limestone, primitive limestone, &c, ac- 

 cording as they happen to suppose any particular specimen 

 they meet with in India to be one or other. The limestone 

 so abundant in Kemaon, as to form the greater portion 

 of that mountainous district, is so much like the lime- 

 stone of the coal measures at Cherra Ponji, that no one 

 unacquainted with the peculiar relations of the two rocks 

 would suppose them to be at all different. The geo- 

 logist however perceives the vast difference between them 

 at once; the one reposes on clay slate, the other on sand- 

 stone ; the one occurs in thick continuous beds, the other al- 

 ternates with shale ; the one abounds in fossils which scienti- 

 fic men alone would think of looking for, and in the other 

 the geologist alone would know that he might look for fos- 

 sils in vain. Speaking of the difference between the limestone 

 of the Silurian system and that of Coalbrook dale, Mr. 

 Murchison says that the organic remains which are in great 

 profusion in the latter, consist of shells and corals which are 

 characteristic of the carboniferous limestone in many other 

 parts of Great Britain, and never occur in the inferior lime- 

 stones of the Silurian system. Among these the most pro- 

 minent are the large Productus hemisphericus and many corals, 

 including hithodendron sexdecimale (Clodocora of Ehren- 

 berg) which is so abundant that it constitutes the greater 



