A HISTORY OF NOTTINGHAMSHIRE 



new deposit. That there are two distinct masses is shown by the section 

 at Shireoaks containing a lower band of 48 feet and an upper band of 

 40 feet separately recorded. 1 In south Yorkshire these two beds are not 

 only recognized but named ; the lower being 1 20 feet thick and the 

 upper one, named the ' small-grained dolomite,' 200 feet. 2 It is to the 

 latter of these the small-grained dolomite that the limestone north of 

 Mansfield belongs. It is possible also that to the same portion belongs 

 the main Magnesian Limestone in the borings to the east of the county, 

 the lower portion having more or less degenerated into shales and thin 

 beds and so being included in the abnormally thick basement beds. In 

 one boring there is a ' sandstone 20 ft.' in a position which would then 

 correspond to that of the Mansfield freestone. 



THE MARLS AND SANDSTONES. Overlying the Magnesian Limestone 

 is found a series of beds consisting of so-called marls (though not calcareous) 

 and sandstones alternating. The latter are chiefly found near the base of 

 the series or in the north of the county. The marls are a brilliant red 

 with bands of bluish white. The sandstones are reddish purple, sharp 

 grained and sometimes calcareous. In most places these have every sign 

 of conformity to the rocks on which they lie ; nevertheless they must in 

 the course of their range overlap the upper part of the limestone to lie 

 on the lower. In some places, as near Mansfield, it has been thought 

 that unconformity may be seen by the undulating surface on which the 

 marls rest. 3 A still more remarkable case is the apparent anticlinal of 

 the limestone overlaid by horizontal marls in a cutting of the Lancashire, 

 Derbyshire and East Coast Railway at Warsop Colliery junction, figured 

 by Mr. C. Fox-Strangways, 4 but this, like the others, may perhaps be 

 explained by an original inequality of the surface and the formation of 

 concentric cracks by subsequent concretionary action. 



The marls do not give rise to any features, but form the base of 

 flat areas, as in the Leen valley. They nevertheless play an important 

 part in relation to other beds. As an impervious stratum of sufficient 

 thickness not to be easily broken through they hold up the water that 

 falls on the overlying porous Bunter sands, and render possible the exist- 

 ence of lakes, as at Newstead and Welbeck, and to some extent also the 

 higher ones at Thoresby and Clumber. On the other hand their softness 

 and comparative thinness has caused them to be removed from over a 

 large surface of the Magnesian Limestone, and gives that more valuable 

 stratum a larger superficial area than its thickness would suggest. 



At the Cinderhill brickworks, in the south of the range of this 

 series, the Magnesian Limestone is seen at the base, followed immedi- 

 ately by the highly contrasting brilliant red clay, in which there are 

 thin beds of sandstone, having their surface covered with curious 

 markings which may be due to annelids. The total thickness here 



1 Lancaster and Wright, loc. cit. 



2 Kirkby, Quart. Journ. Geol. Sac. vol. xvii. 



3 Geol. Survey Mem. sheet 82, S.E. 



4 Quart. Journ. Geol. Soc. vol. liv. p. 161, fig. I. Compare fig. z. 



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