78 Rev. A. Sedgwick on the Geological Relations and 



similar instances, though perhaps exceptions to the more usual character of 

 the contemporaneous deposits in our country, seem to confirm the conclusion 

 which I have endeavoured to establish. 



Foilowino^ the mac^nesian escarpment from the rail. road above mentioned towards the north, 

 •we frequently lose all traces of the marl-slate and thin-bedded compact limestone. They may, 

 however exist in many places under the incoherent matter which disguises the lower part of the 



terrace. 



A quarry in the hill above Coundon lays bare the bottom beds of limestone. They are thin 

 and almost slaty, and of a smoke. grey, ash-grey, and blue colour. Some of them are earthy ; 

 but others arc almost compact, and contain crystalline nodules of sulphate of barytes, with sul- 

 phuret of lead and sulphuret of zinc irregularly disseminated through their mass. Their position, 

 texture mode of bedding, and association with metallic sulphurets, clearly identify them with the 

 compact limestone of East Thickley and Midderidge. 



In several parts of the escarpment between the last-mentioned locality and the banks of the 

 Wear, I have found thin beds of impure sandy marl-slate between the magnesian limestone and 

 the lower sandstone. And in the sinkings of the Hetton pits, as also in the wells near Sunder- 

 land, the same beds have been found associated with thin layers of blue and nearly compact lime- 

 stone. 



Some of the natural sections on the south bank of the Wear exhibit distinct traces of the marl- 

 slate immediately under the great shapeless beds and masses of magnesian limestone ; and there 

 can I think, be no doubt that the whole quarry at Pallion is very nearly connected with it. For 

 we there find a system of strata which are chiefly composed of thin and nearly compact masses of 

 light ash-grey, and srnoke-grey limestone, separated by, and mixed with, various marls and thin 

 beds of yellow marl-slate : and in the lower part of the section are some thicker beds, with 

 various shades of light. grey, ochre-yellow, and blue, which contain very little magnesia. Some 

 of these lower beds are almost compact, and near the bottom of the quarry are of so fine a 

 texture that they were formerly worked for marble. The discovery of a fossil fish in these 

 quarries further lends to identify them with the formation of marl-slate and compact limestone, 

 though their mineral character somewhat differs from its usual type*. 



The only part of the escarpment between the Wear and the Tyne which exhibits these inferior 

 beds in a characteristic form, is at West Bolden. We have there a section nearly fifty feet high, 

 which exhibits about thirty feet of thin slaty beds resting on the lower red sandstone, and sur- 

 mounted by about twenty feet of hard amorphous cellular masses of yellow limestone f. The slaty 

 beds possess an intermediate character between the varieties of marl-slate and compact limestone 

 above described. They are generally of a yellowish brown colour ; and they are almost covered 

 with black dendritic impressions. It is difficult to obtain a clear cross fracture from them ; for 

 they separate at a number of transverse natural joints, which are also covered with a similar den. 

 dritic coating. 



To the north of the Tyne, the two outlying masses at Whitley and Cullercoats may perhaps 

 both be referred to the marl-slate and compact limestone. The several beds at the former locality 

 have been already described in the Society's Transactions (First Series, vol. iv. p. 6). Some of 



* For some further details respecting the Pallion sections, see a paper by Dr. Clanny, Annals 

 of Philosophy, vol. vi. p. 115, &c. ; and Mr. Winch, Geol. Trans. First Scries, vol. iv. p. 9. 

 t See Plate VII. fig. 2. 



