internal Structure of the Magnesian Limestone. 69 



the incoherent materials which have descended from the upper part of the escarpment • but a 

 series of strata are laid bare in a hollow road nearly in the following order, beginning with the 

 lowest. 1. Beds of loose micaceous sand with grey sandstone partings; whole thickness not ex- 

 posed. 2. A freestone about fourteen feet thick, very irregularly bedded, and variegated; some 

 parts being light grey, and others greenish red with cloudy spots. 3. Beds of sandstone and 

 sandy shale, with some partings of ochreous marl. 4. Beds of bluish marls, with bands of 

 variegated and red micaceous freestone. 5. Red and yellow marls immediately under tlie lime- 

 stone. If the whole system of these beds were laid bare, their united thickness would probably 

 amount to more than one hundred feet. 



In following the remaining part of the escarpment as far as the river Went, it appears to re- 

 cover its more usual characters ; as the portions of it which are vi&ible consist of coarse-grained 

 sandstone, more or less stained with red oxyd of iron, and of slaty micaceous sandstone, generally 

 red and variegated; alternating with, and surmounted by, marls of the same prevailing colours. 

 In one or two places (especially on the line of the road from Doucaster to Wakefield), it spreads 

 out considerably to the west of the limestone, and forms a low but well-defined escarpment. 



Again, between the valley of the Went and Pontefract the deposit becomes of greater thickness 

 and more complex structure ; containing much incoherent micaceous sand, which, by its dogra^ 

 dation, forms a narrow zone of light unproductive soil in the lower part of the terrace, between 

 the limestone and the highest beds of the coal formation. 



Immediately round Pontefract it is well exposed in several characteristic sections, especially 

 under the regular escarpment which ranges on the south-east side of the town, where several 

 quarries have been opened in a coarse grey sand and sandstone, which is micaceous, irregularly 

 bedded, partially tinged with red, and contains a few concretions of hydrate of iron, but does not 

 exhibit any of the usual red, blue, or variegated marls. The soft yellowish grey sandstone under 

 the Castle must be referred to the same formation, as well as several of the sandstone quarries 

 near the south-western extremity of the town. There is, however, a peculiar difficulty presented 

 by some of these localities, arising out of the absence of the separating marls, and the apparently 

 gradual passage of the sandstone into the limestone, which makes it almost impossible to ascertain 

 their precise limits. The difficulty does not, however, end here ; for on the road leading from 

 the outskirts of the town towards Wakefield, a strong yellowish brown siliceous grit (which, if 

 I have not been misinformed, has been proved by boring to the depth of at least eighty feet) ap- 

 pears below all the beds before described. At first I took for granted that the whole mass of 

 this grit represented the lower portion of the inferior red sandstone ; but a subsequent examina. 

 tion of the strata at High Field colliery, a few miles north of Pontefract (where the several beds 

 were cut through by a pit sunk in the year 1823, from the magnesian limestone to the coal- 

 measures), made me at least doubt the propriety of this conclusion*. I have been the more par- 

 ticular in referring to these sections, as Mr. Smith designates the formation I am attempting to 

 describe by the name Pontefract Rock, — a term which ought on no account to be retained ; 

 because the sand rock, for the reasons above given, is not there developed in a manner sufficiently 

 distinct and characteristic to be considered as a good general type of the deposit. 



After the terrace crosses the Air, there are for several miles no denudations which exhibit tlie 

 junction of the magnesian limestone and the coal-measures. But in various parts of the low 

 terrace which extends by Kippax and Church Garforth towards the Abberford rivulet, we have 



* See the High Field section, ante p. 58. It is, I believe, impossible in that section to draw 

 any well-defi.ned line between the lower red sandstone and the coal-measures. 



