internal Structure of the Magnesian Limestone. 47 



Tunstall, It is also seen under thirty or forty feet of diluvium on the right bank of the Swale 

 about half a mite above Catterick Bridge*. These indications of the magnesian limestone, vfhich 

 are not noticed in the map of Yorkshire, seem to prove, that the formation was once continued 

 (though probably much below its mean elevation) from Wallas to the river Swale. Indeed it ap- 

 pears to be generally true in our island, that the actual elevation of ail the beds subordinate to 

 the new red sandstone is greatly modified by the height of the formations on which thej have been 

 deposited in an unconformable position ; and beyond Watlas there was probably no elevated rido-o 

 of the carboniferous beds to form the support of the magnesian terrace. 



In the flat country to the north-east of Catterick Bridge, and along the eastern skirts of the 

 mountain limestone hills near Middleton Tyas, there are no traces of the magnesian limestone. 

 The formation may, however, in some places be disguised under the immense masses of gravel 

 which are spread over the lower portions of the district f. Following the general bearing of the 

 range, it reappears in a hill about halfway between Newton Morrel and Cleasby. From thence 

 it is probably continued under the mounds of diluvium near Manfield ; for it is seen again on the 

 south bank of the Tees below Pierce Bridge, and stretches on the same side a little way above 

 the bridge, where it is capped with about thirty feet of diluvial gravel. Oj» the same bank of the 

 Tees and west of the Catterick road, it is seen in a highly characteristic form at Rennison quarry 

 near Eppleby ; and I am informed that it was discovered in sinking a well on the south part of 

 Lowiield estate, and also at Chapel Houses a little to the west of the former place +. Whether 

 these are separate patches of the magnesian limestone, or parts of a continuous mass, it is impos- 

 sible to determine in the present state of the denudation. 



After the formation enters the county of Durham, it continues to occupy for several miles a low 

 tract of country ; and, on its north side, appears to abut against a high irregular ridge of sandstone, 

 which ranges through Bolam and Brussleton Tower. Under such circumstances the boundary 

 can only.be defined by determining a number of places which are on the western limits of the 

 formatipjj'. I venture however to hope, that the following details will give the line of demarca. 

 tion as nearly as the nature of the country admits. This line crosses the Tees immediately at 

 Pierce Bridge, and extends on the north bank of the river into the rivulet which descends from 

 Killaby. After ascending some way in the course of that rivulet, it appears to bear through the 

 flat district in a north.v^'esterly direction, encloses Headlam, and may be traced into some quarries 

 between HoHin Hall and Langton. Langton, Ingleton, and Morton Tinmouth, are all situate 

 on low hills, which are just skirted by the flat region of the limestone : and from the last of these 

 places the line ranges nearly due east, skirting the soutii side of the ridge which extends to 

 Iloughton-le-Side ; close to the south-east end of which place, the limestone is seen in some 

 quarries abutting against the sandstone. 



* Some beds of yellow marl, said to have been sunk through in excavating the ground near 

 Hornby Church, may probably belong to the magnesian limestone ; but I had no opportunity of 

 examining them. 



t I have been informed that wells, twenty or thirty feet deep, were sunk through the gravel at 

 Scorton and Uckerby without touching the yellow limestone. At Moulton a variety of limestone 

 is brought out by a flexure of the strata, which, from its colour and mineralogical character might 

 be easily mistaken for a fragment of the magnesian limestone formation. Its fossils and the beds 

 associated with it, plainly demonstrate it to be a variety of mountain limestone. Many other parts 

 of the ridge which extends from Middleton Tyas to the north-west, partake of the same minera- 

 logical character. 



X The limestone of Low Field and Chapel Houses may, perhaps, belong to yellow magnesian 

 varieties of the carboniferous limestone ; for beds of that character occur at no great distance 

 from these localities. 



