Murchisoris Silurian System. 27 



bury, are much obscured by a thick cover of coarse gravel 

 and clay. In other situations north of the Severn, the calca- 

 reous conglomerate of the New Red System contains angular 

 fragments of cream-coloured limestone, in a reddish sandy 

 calcareous matrix, in which small cavities occasionally occur 

 lined with crystals of dolomite. Limestone containing mag- 

 nesia is abundant in some beds of mountain, or carboniferous 

 limestone in the same vicinity, and that rock being of older 

 date, may have supplied many of the enclosed materials, and 

 much of the cement of this conglomerate." 



Some fragments of limestone of large size, derived from 

 the breaking up of a peculiar fresh water limestone interca- 

 lated between seams of coal, are also contained in it, as well 

 as small round quartzose and other pebbles of more ancient 

 rocks. Although Mr. Murchison observes it has been stated 

 in the previous pages that no remains of shells have yet been 

 detected in the overlying members of the New Red System 

 in England, a considerable number of curious unpublished 

 species have recently been discovered at Manchester in beds 

 of the variegated marl. These shelly marls are considered 

 by Professor Sedgwick to lie beneath the upper and central 

 members of the New Red System, and Professor Phillips, 

 who has recently worked out in some detail the relations of 

 strata in the environs of Manchester, is of the same opinion. 

 In a letter to Mr. Murchison, he describes these shelly 

 marls as lying between the sandstone and quartzose con- 

 glomerates, gres higarre, and the lower beds of the New 

 Red System, and observes, " I view them as attenuated and 

 deteriorated magnesian limestone, the last term of the de- 

 gradation of this rock ;" it is therefore inferred that the Man- 

 chester shelly beds are of the same age as the calcareous 

 and dolomitic conglomerates of Salop, Worcester, and Staf- 

 ford, which are the equivalents of the magnesian limestone. 



These marls are said by Mr. Murchison to be of great 



