76 Rev. A. Sedgwick on the Geological Relations and 



our own formations into a nearer accordance with tliose of the same age in 

 central Germany ; but I have followed an arrangement which is borne out by 

 many natural sections. At the same time it must be allowed that this deposit 

 is, with local exceptions, very imperfectly developed ; that it often does not 

 admit of any well-defined line of separation from the beds which are superior 

 to it • and that it is probably contemporaneous with some of the lower beds of 

 ma"iiesian limestone which frequently occupy its place without exhibiting the 

 same mineralogical characters. 



The o-roup I am describing is seen in a very characteristic form on the side 

 of the Stockton rail-road, at the quarries of Midderidge and East Thickley. 

 In the construction of that work a series of beds was cut through, which pre- 

 sented the following phaenomena, commencing with the lowest part of the 

 quarries. 



1. Beds of light-coloured siliceous sandstone, worked as a coarse flagstone 

 and also as a building stone. The upper beds alternate with a blue-coloured 

 calcareous shale. At East Thickley they are about thirty feet thick. 



2. Yellow-coloured calcareous shale and marl-slate, in thickness about nine 

 feet. Some of these beds are incoherent and sandy ; the marl-slate forms a 

 series of indurated bands which divide the more incoherent shale. 



3. A series of thin beds with marly partings ; the whole about twenty feet 

 thick. The average thickness of the several beds is not more than a few 

 inches ; their surfaces are often coated with yellow marl ; at their natural 

 partings they are generally covered with dendritical impressions. Not un- 

 frequently in their interior they pass into a nearly compact limestone, the finer 

 specimens of which have a conchoidal fracture, are translucent at the edges, 

 and exhibit a smoke-grey, yellowish, or bluish colour. The separation of these 

 beds can seldom be represented by a plane surface : but on the removal of 

 any of the upper strata, we may generally observe a number of spherical pro- 

 tuberances, which indicate a more or less perfectly concretionary structure. 

 The fracture of the more compact beds seldom gives any indication of this 

 structure ; yet when viewed externally and on a considerable scale, they may 

 be said to resemble a number of spheres which have been placed side by side, 

 and afterwards have been compressed and partially melted into each other. 

 Over all the preceding come the ordinary beds of coarse yellow magnesian 

 limestone. 



The beds described in the preceding section appear to contain very little 

 magnesia ; indeed some of the beds of indurated marl-slate and compact 

 limestone do not exhibit a trace of it. Some of the compact beds are, how- 

 ever, partially cellular, like the magnesian limestone, and have their cells lined 



