162 DESCRIPTION OF THE STRATA. 



breaking into numerous indeterminate fragments ; and some, solid 

 and massive. Like the alum schist, it usually increases in solidity 

 as it descends. Its colour is sometimes a deep red, like the darkest 

 red ochre ; but the most common colour is a brick red, of various 

 shades. This passes into a very pale red, and that again into yellow ; 

 which in many places, especially in the lower beds, changes to white, 

 or yellowish white. These colours are not always in distinct layers, 

 but are often clouded or blended together. The rock frequently 

 contains hard bands of grey sandstone, and stripes or seams of a 

 greenish blue substance, partly clay and partly lime. Calcareous 

 matter is indeed so generally diffused through these strata, that most 

 of their varieties effervesce with acids. The red and yellow colours 

 are probably owing to a mixture of ferruginous or ochrey matter. 

 Balls of ochre and nodules of ironstone appear to exist in some parts 

 of the strata. We may add, that as the red rock is supposed to be 

 indebted for its colour to oxide of iron, so the greenish stripes are 

 considered as deriving their hue from oxide of copper.* 



Owing to the thickness of the alluvium that covers the plain of 

 Cleveland and the vale of the Tees, there are few places where these 

 strata are exposed to view ; and such places are almost all in the 

 channels of the Tees and the Leven. The red sandstone may be seen 

 in the bed of the Tees, at Croft bridge near Darlington, and at some 

 distance to the westward of that bridge. It may be seen not far from 

 the western skirts of the highest of our alum hills, in the bed of the 

 Leven, below Crathorne ; particularly at a mill a little below Foxton 

 bridge, and at Middleton mill dam, near a mile lower. At the latter 

 place, we find the yellow sandstone along with the red. The same 

 strata appear further down, about Leven bridge not far from Yarm, 

 and from thence to the Tees. The channel of the Leven, in most of 



* Geological Transactions, I. p. 191, 193. 



