A. IRVING ON SOME EECENT SECTIONS NEAR NOTTINGHAM. 515 



the latter varying in thickness from one to four and five feet. One 

 of these, with a colour approximating nearly to white, is charac- 

 terized by numerous cavities, without any definite form or arrange- 

 ment, which are probably to be accounted for by the dissolving away 

 of calcareous concretions previously existing in the sandstone, by 

 infiltrations of water charged with carbonic acid. About the middle 

 of tho Waterstone Series, the sandstones and shales arc replaced by 

 a kind of sandstone, in which the fine siliceous and argillaceous 

 materials are intimately intermingled. At an horizon somewhat 

 lower the sandstones are more purely siliceous, with numerous inter- 

 stratified bands and thin marl-partings. The surfaces of these have 

 received numerous ripple-marks, rain-pit tings, and sun-cracks — 

 many hundreds of truck-loads of such marked slabs having been 

 brought up from the tunnel which penetrates underneath the 

 Mapperley " Plains " to the north-east of Nottingham, at a depth 

 below their highest point of 180 feet. 



Though no fault is intersected by the railways, there are never- 

 theless some rather large ones in the Keuper strata of the district, 

 the result, as I take it, of increased dislocation of the subjacent 

 palaeozoic strata in post-Triassic times. One such fault is exposed in 

 the face of the cliff which overhangs the railways at Colwich, and 

 has a throw of not less than 100 feet. On the east side of it are 

 the upper marls of the Upper Keuper, with many bands of gypsum ; 

 on the other side of tho fault are the sandstones of the Lower 

 Keuper, which exactly correspond with the lower portion of those 

 pierced by the Mapperley Tunnel. As this fault runs north-west, 

 but not precisely in the direction indicated on the Survey-map (the 

 effect of its throw being reversed by a second fault between it and 

 the railway above described), it is exposed in several places. At two 

 points, (1) at Blue-bell Hill, (2) at the top of Red Lane, where 

 this joins the Mapperley Road, the fault forms what must have once 

 been an open gaping fissure : at the first-named place, its width is 

 11 yards ; at the latter, 15 yards. In both instances the fissures 

 are filled with debris of Keuper strata broken up into a confused 

 rubbly mass by drift action. 



