NORTHUMUERLAND AND DX7EHAM. 21 



grovips. Generally, the Magnesian Limestone was a pelagic de- 

 posit, with, however, evidences of shallow water at intervals, 

 and alternations from a deep sea to an estuary. 



Some plants affect a Magnesian Limestone soil. Sedgwick 

 says, that so characteristic is Brachypodium pinnatum of that 

 soil, that by its help he could trace the yellow limestone with 

 great exactness ; but it has not been found within our district. 

 The following are peculiar Magnesian Limestone species : Linum 

 perenne, Hypericum montanum, Carduus eriophorus, Orchis pyra- 

 midalis, Ophrys apifera, Ophrys muscifera, Cypripedium calceolus. 



MESOZOIC ERA. 

 V. TRIASSIC FORMATION. 



Eed sandstones overlie the Magnesian Limestone in Durham 

 and pass under the Lias of Cleveland. They are much obscured 

 by a covering of drift, and fossUs have not been found in them ; 

 hence their extent cannot be traced with exactness, nor is their 

 synchronism determinable with certainty. Still, from their rela- 

 tive position, and their mineral character, they may be referred 

 to the Trias, which forms the substratum of the great central 

 plain of England. The lower beds are generally coarse in the 

 grain, and of a brick red colour, and sometimes marly ; and above 

 these are gypseous marls. Sections of them appear on the coast 

 near Seaton Carew, and on the banks of the Tees. Unsuccessful 

 sinkings were made through these beds in search of coal; but 

 though 444 feet were gone through at Dinsdale, and 708 feet 

 opposite Sockburn, the Magnesian Limestone was not reached. 



These beds occupy the flat country in the south-eastern part of 

 Durham from Hartlepool to the Tees, with an extension west- 

 ward of 17 miles. The whole area is about 180 miles. 



CAINOZOIC ERA. 



No hard stratified rocks more recent than the Trias appear in 

 our district ; but over a considerable portion of it, excepting on 

 the higher grounds, there are accumulations of clay, gravel, and 

 sand in layers of irregular thickness and extent. The exact 



