226 CATALOGUE OF THE FOSSILS OF THE PERMIAN SYSTEM 
distance south of Castle Eden Dene the cliff presents the same 
laminated and brecciated beds as are seen at Marsden. At 
Black Halls the limestone sinks below the surface, and is not 
seen again on the coast, but in the mass on which Hartlepool is 
situated, several beds occur in the cliff-section, which are com- 
posed of concretions so small and regular that they perfectly 
resemble true ovlitic rocks. In the south-eastern part of the 
county the beds of Magnesian-limestone are succeeded by a de- 
posit of reddish sandstone and marl, which are supposed to be- 
long to the “Upper-new-red-sandstone.” These are generally 
concealed beneath heaps of alluvial clay and rubbish, and can 
only be examined in a section or two on the banks of the Tees, 
and another on the coast near Seaton. 
The bed of limestone in which most of the marine remains 
peculiar to this system are found, and which by way of eminence 
may be styled the fossiliferous, is first seen capping the low- 
rounded hill, umbleton, on the south side of the Durham and 
Sunderland road. It is here of considerable thickness, very hard, 
and somewhat crystalline, though some portions of it are earthy 
and rubbly. More or less changed in appearance in each of the 
following localities, it is preseut in the series of low hills which 
range from Ilumbleton Hill by Silksworth, and Tunstall Hill to 
Ryhope, Dalton-le- Dale, and Hawthorne Hive, where the line is 
broken by the coast. It must be observed that the fossils are 
not equally distributed throughout this bed. In some parts of it 
there are no traces of them, but other parts are entirely composed 
of shells, broken corals, and encrinital stems matted together. 
In Humbleton quarry, when the shell is preserved, the outer sur- 
face is nearly obscured by a thin coating of lime, but most fre- 
quently the casts only remain, the shell falling to pieces imme- 
diately the stone which contains it is broken. In this case a 
cast of the outer surface of the shell is contained in the matrix. 
At Tunstall Hill the limestone is very hard and crystalline. 
The outer surface of the shells imbedded in it are generally well 
preserved, and they are either filled or lined internally with 
crystals of carbonate of lime. At Silksworth and Dalton they 
are either in casts or with the shell well preserved. In the lat- 
