groups. Generally, the Magnesian Limestone was a pelagic deposit, 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 pyramidalis, Ophrys apifera, Ophrys muscifera, Cypripedium calceolus.
MESOZOIC ERA.
V. TRIASSIC FORMATION.
Red sandstones overlie the Magnesian Limestone in Durham and pass under the Lias of Cleveland. They are much obscured by a covering of drift, and fossils have not been found in them; hence their extent cannot be traced with exactness, nor is their synchronism determinable with certainty. Still, from their relative 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 westward 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
