SECONDARY LIMESTONE. 439 



a great variety of appearance, depending on the 

 colours, proportions, intermixture, and size, of 

 the parts ; and these, like the primary calcareous 

 rocks which exhibit similar features, are some- 

 times wrought as ornamental marbles. 



Conglomerate limestones are also found among 

 them, consisting of a basis of calcareous matter 

 with imbedded fragments of older rocks ; and 

 these are not unfrequently interposed among the 

 strata of the lowest red sandstone. Calcareous 

 conglomerates also occur in the upper limestones 

 of the west of England, which seem to correspond 

 to the magnesian limestone of the north-eastern 

 district. As these are necessarily treated of again 

 under a distinct head, the present brief notice of 

 the fact will in this place suffice. 



The texture of secondary limestones, like that 

 of the primary, is very various. They are some- 

 times earthy, like chalk, or else somewhat more 

 compact, and presenting a dull, but even, fracture, 

 like that of the non-fissile argillaceous schists or 

 clay stones. Such earthy limestones are com- 

 mpnly of a very fine texture, but, occasionally, 

 they have a coarser or an arenaceous appearance. 



