88 MR. R. L. SHERLOCK ON THE RELATIONSHIP OF THE [Feb. I9I I, 



In the Geological Survey Memoir Aveline figures (op. cit. p. 17), 

 from information received, an unconformable junction of the 

 dolomitic sandstone with the red marl. 



If the sandy bands iu the Marl continued to increase westwards, 

 it is clear that a sandrock would result, which might be easily 

 regarded as Bunter ; and this would rest directly upon the dolomitic 

 sandstone with apparent unconformity. 



An old pit for potter's clay, situated close to the railway-bridge 

 over the Nottingham Road, shows that the Permian Marl still 

 persists, although the outcrop has become very narrow. At 

 Littleworth, a section close to the Brewery shows 8 feet of sand- 

 rock with a 3-inch band of marl very near the Limestone : hence 

 there is not room for more than a few feet of marl, if any, between 

 the two. Farther north, sandrock can be seen resting un conform ably 

 upon the dolomitic sandstone below the level of the track of the 

 Midland Railway, east of Crow Hill (Mansfield) ; and there is a 

 good section, showing similar conditions, at Hallam's Grave, north 

 of Mansfield. 



Origin of the Mansfield Dolomitic Sandstone. 



It seems probable that the local great increase of sandiness in 

 the Magnesian Limestone, and in the Permian Marl above it, have 

 a common cause. Sedgwick 1 inferred that the sandy development 

 of the limestone is confined to the Mansfield district ; but this 

 statement must be modified slightly, as very sandy limestones occur 

 in places north of Warsop. However, the fact remaius that the 

 Mansfield Sandstone is almost, if not quite, unique. 



On attempting to map the dolomitic sandstone, it is found that, as 

 it is followed north-eastwards along the strike, it ceases to remain 

 at the top of the Limestone, but becomes overlain by dolomite, into 

 which it passes upwards gradually, as, for example, at the Rock 

 Yalley quarries ; and the same conditions are noted if it is followed 

 north-westwards, across the strike. At the Chesterfield Road 

 quarry, one mile north-west of Mansfield, and in the very deep old 

 quarry in Debdale Lane, the 'sandstone' is seen at the bottom of 

 the quarries passing upwards into dolomite. Also at the Chester- 

 field Road quarry the limestone has been proved underneath the 

 ' sandstone,' which is about 50 feet thick. The sandstone does not 

 crop out again until Pleasley Yale is reached, when it appears at 

 the very base of the Magnesian Limestone, with the grey Lower 

 Marls alone beneath it. It is clear, then, that the sandstone cannot 

 lie at one horizon, but that it is a lenticular mass tilted in a 

 direction opposite to the dip of the beds. If the lenticular mass 

 extends in an easterly, as it does in a westerly, direction, the tilt 

 will carry the sandy conditions into the Permian Marl ; and this at 

 once explains the apparent absence of the Marl at Mansfield, as it 

 is there represented by sandy beds which merge into the Bunter 

 sand above. 



1 A. Sedgwick, 1829, pp. 83-84. 



