HAUL- SLATE AND LOWER MAGNESIAS LIMESTONE. 199 



Gervillia antiqua, Terebratula saccula (elongata), Stenopora colum- 

 naris, Trochammina pusilla, and a Bryozoan that was not deter- 

 minable. The two beds in which these fossils occnr may almost 

 be said to form the base of the Magnesian Limestone proper ; the 

 next Wo feet or more being, as it were, passage beds from the 

 Marl-slate to the limestone. i 



I would remark, that it is not every section of these two mem- 

 bers of the Permian Series that shows so intimate an interblending 

 as the one nnder notice. In many places the junction of the 

 Marl-slate with the Lower Limestone is sharp and well marked. 

 This is the case at Claxheugh, at Hartley's Quarry, at Fulwell 

 (water works), at Down's Quarry, near Hetton, and at other 

 places. By examining such sections as the latter only it might 

 easily be thought that the break between these members is more 

 abrupt than it really is. The intercalation of bands of Marl-slate 

 with beds of limestone at Offerton and other places indicates, as 

 far as the geology of the case is concerned, that the change in 

 physical conditions took place gradually. And though, as all 

 palaeontologists are aware, the fossils of the Marl-slate form a 

 distinct group from those of other portions of the Series, they 

 nevertheless offer one or two facts supporting this idea. In some 

 localities where Lingula and Distinct, occur in the Marl-slate, 

 along with the more characteristic fossils of that deposit, they 

 are found to pass up for three or four feet into the overlying 

 limestone. And at Pallion, as already noticed, Platysomus stria- 

 tus is also found in the limestone along with shells more properly 

 belonging to that member (p. 196). 



Bough Dean.— Four miles to the S. of the last described loca- 

 lity, in Bough Dean, to the SE. of Houghton-le- Spring, a similar 

 limestone occurs in the same relative position. The section is 

 exhibited on the north bank of the rivulet, a little to the east 

 of the Hetton Bailway. Commencing from above, it runs as 

 follows : — 



FT. IN. 



Gravel, sand, and boulders 10 



1. Hard, yellowish brown limestone, full of patches of 



calc spai', in three beds , 2 10 



