RED SANDSTONE WITH GYPSUM. 167 



spa, has lately acquired some celebrity, as a place of resort for 

 invalids. A similar spring issues from the same strata at Croft bridge, 

 on the south bank of the Tees, which is also a place of resort in. 

 the summer months. 



It is natural to expect sulphuretted springs, in strata that contain 

 so much gypsum, or sulphate of lime. The same kind of strata in 

 Somersetshire contain also sulphate of strontian ; and were our strata 

 less concealed by alluvium, quantities of the same mineral might be 

 found here also. It is said, indeed, to be found on the banks of the 

 Nidd near Knaresborough ; not, however, in the red sandstone, but 

 in the limestone.* 



The rock salt of Cheshii'e and Worcestershire is imbedded in 

 strata corresponding with those of the vale of the Tees ; but no brine 

 springs have been discovered in our district. There is a salt spring- 

 issuing from the interstices of a basaltic vein, in the bed of the Wear 

 at Butterby, two miles to the south of Durham ; but it is too far from 

 our red strata to have any connection with them.t 



The deep alluvial covering of this member of our strata, pre- 

 vents us from giving an accurate view of its extent. It appears, 

 however, to occupy almost all the plain of Cleveland, with a con- 

 siderable portion of the north bank of the Tees ; and as it extends to 

 the westward of Croft bridge, so it proceeds round the west skirts 

 of our oolite hills, by Northallerton and Thirsk, near which are some 

 gypsum quarries ; and from thence it is supposed to advance further 

 south into the vale of York. 



The occurrence of the red sandstone in the plain of Thirsk, not 

 far from the west front of the Hambleton hills, naturally leads us to 

 conclude, either, that our aluminous strata which are of a vast 



* Geological Transactions, III. p. 370, &c. IV. p. 196, 202, 214, 445. 

 t Ibid. 1. p. 38, &c. II. p. 94, &c. IV. p. 24. 



