internal Structure of the Magnesian Limestone. 53 



Hills of magnesian limestone, nearly bounded by the natural drainage of the country, rise on 

 the north side of Rushy Ford, but are cut off by a valley of denudation descending from Thris. 

 lington. Along the course of this deep valley the whole formation has apparently been swept 

 away. Beyond this denudation the main branch of the Skerne passes to the south of all the places 

 where the limestone appears at the surface. 



About Embleton and Elwick the ridges of diluvial hills above described entirely bury the for- 

 mation ; but in the rising ground to the south of Hart, the limestone is again uncovered and the 

 demarcation maybe traced on the south side of Throston, and on the south side of Dyke House 

 till it is lost in the blown sand at the head of Hartlepool Slake. From Hartlepool to the mouth 

 of the Tyne the magnesian limestone, as is well known, is the only rock which is visible on the 

 coast, and is only interrupted by some inconsiderable cliffs, principally composed of blown sand 

 which appear to the north of the peninsula of Hartlepool, and near the mouths of the Wear and 

 the Tyne. 



§ 4. Outliers of the Magnesian Limestone. 



After the preceding details respecting the range and external characters of 

 the formation, it remains for me to notice the outliers which appear to the 

 west of its escarpment. 



A more careful survey of the county of Nottingham may perhaps lead to the discovery of some 

 outliers of the yellow limestone, as there are several places where its western limit is ill defined. 

 In the range through a small part of Derbyshire it makes a well-defined escarpment. In York- 

 shire, notwithstanding the deep indentations of the escarpment, there is no outlier to the south 

 of Conisbrough. A deep valley of denudation (which passes through a part of the village, and 

 communicates with the Don) cuts off a plateau of the magnesian limestone. This outlying mass 

 ranges from the crest of the hill immediately south-west of the castle, and from thence along the 

 brow of the hill which overhangs the new road to Rotherham. The capping of limestone gradually 

 disappears towards the south, without forming any regular escarpment : but a projecting tongue 

 of the formation extends on the south-west side into the quarries of Hooton cliff, about half a 

 mile from the village. The west and north boundaries of the remaining parts of this outlier are 

 well defined, and are correctly delineated by Smith. On this plateau there is, if I mistake not, 

 a second outlier; for a small, and apparently unconnected, patch of limestone breaks out from 

 beneath the soil, in the fields about two hundred yards south of the turnpike gate. (See 

 Plate I. No. 4.) 



Following the range of the limestone towards the north, the next outlier is at Pontcfract. It 

 crowns the castle hill, extends through the town, caps the hill on the right of the road leading to 

 Wakefield, and also the first hill beyond the outskirts of the town on the Doncaster road. If 

 the colour were extended a little further to the south, the delineation of this plateau in the map 

 of Yorkshire would be correct. There is, however, a very unusual difficulty in this delineation, 

 arising out of the obscure separation of the limestone and the inferior sandstone : and as the 

 capping of the upper formation appears to rest on an uneven surface, the plateau is perhaps com- 

 posed of more than one outlier. 



Three remarkable round-topped hills, composed of magnesian limestone, stretch in a south- 

 westerly direction from the village of Kippax to Great Preston. The first of these hills (in con- 

 sequence of a grel^fault which throws the Kippax limestone below its mean elevation) is probably 

 connected with the escarpment of the formation, and cannot therefore be considered as an outlier. 



