540 CO. 1. Trechmann—Brachiopods from Durham. 
so plentifully until a few years ago while the underlying sandstone 
was being quarried. 
Dr. Coggin Brown found here a specimen of the teeth and shagreen 
of Janassa bitwminosa Schloth. some years ago when he and I were 
collecting in the Marl Slate at this place. 
The Marl Slate passes up rather gradually into the compact 
dolomitic Lower Magnesian Limestone, and this in turn merges up 
into a bed of calcareous limestone, which is fairly thick in the north- 
west end of the quarry, but gradually thins out towards the south- 
east. This is again overlain near the top of the section by dolomitic 
rock very similar to that above the Marl Slate. The dolomitic rock 
appears to have been deposited as dolomite, and is only very sparsely 
fossilifercus, but the calcareous beds have yielded a very interesting 
suite of excellently preserved fossils, to some of which I wish to 
draw attention. 
The calcareous Lower Magnesian Limestones, which consist of 
very pure limestone in South Durham, are of rather unusual interest, 
as they seem to occur as lenticular masses in the dolomite. In many 
Permian sections the whole of the Lower Limestone is dolomitic 
throughout, but in others the calcareous beds attain a considerable 
thickness. 
At Raisby Hill Quarries, near Coxhoe, 9 miles north-east of 
Thickley, they are about 60 feet thick, but are much less fossiliferous 
than at Thickley. In a boring recently put down near Sheraton, in 
South Durham, 6 miles east of Coxhoe, the calcareous beds proved 
to be about 120 feet thick, but no fossils appeared in the cores. 
T have nowhere seen the calcareous Lower Magnesian Limestone so 
fossiliferous as it is at Hast Thickley, and the rock appears on 
examination of weathered surfaces with a lens to be made up of 
organic fragments, though, strangely enough, a thin slice reveals 
practically no structure. I have already published analyses of 
these rocks.1 
Some remarkable blocks of limestone have recently been collected, 
the weathered surfaces of which, after being cleaned and developed, 
show something of the manner in which the Brachiopods lived, 
associated together on the bed of the Permian sea. Two of these 
seem to deserve special attention and illustration. 
The first, represented by a sketch (Fig. 2), exhibits a specimen of 
Productus horridus Sow., bearing on one side two thick slightly 
eurved spines which spring from the ear of the ventral valve and 
measure between 24 and 3 inches in length. Near the end of one 
spine (A) a specimen of Lpithyris elongata Schloth., now rather 
crushed, has fixed itself by the foramen of its ventral valve, the back 
of which is visible on the slab. The oval outline, gently rounded 
surface, absence of median sinus and punctation of the shell in this 
1 “Uithology and Composition of Durham Magnesian Limestones ”’ : 
Q.J.G.S., vol. Ixx, 1914, p. 247. 
