A HISTORY OF NOTTINGHAMSHIRE 



Newark. These peculiarities show that both one and the other division 

 of the Keuper were deposited between tide marks. The same condition 

 of deposit is indicated by the footprint of a Labyrintbodont found on the 

 sandstone at Colwick by Dr. Irving, and the remarkable shoal of ganoid 

 fishes, Semionofus, found stranded all together in one bed at Rough Hill 

 Wood by Mr. Wilson. It is judged from this that, as in the case of the 

 Coal-Measures, the base on which the deposits rested was constantly 

 being depressed at the same average rate as the deposits were formed, 

 but, as these do not contain the ordinary marine fossils, the water was 

 enclosed as a lake and the depression was not sufficient to open this to 

 the sea till the next succeeding epoch. 



At a higher level the sandstones become thicker and of a brown 

 colour. These tend to form escarpments, as at Spital Hill near Retford, 

 at Bothamsall, Kirton, and Belsthorpe and Edingley Hill near South- 

 well. 



The Keuper Marls are distinguished by the preponderance of clay 

 over sandstone and by the vivid red colour of the former. The beds of 

 sandstone are usually thin, but there are parts where each bed is thicker, 

 or where the thin beds are closer together, such as the neighbourhood of 

 Tuxford, where much stone has been extracted for building under the 

 name of the Tuxford Stone. Another important distinction is the 

 abundance of gypsum. This mineral is not unknown in the Keuper 

 Sandstone, where it forms fibrous strings or veins, but in workable masses 

 it is confined to the marls. 



Gypsum is a hydrous calcium sulphate, with a composition (from a 

 Nottingham sample) of: calcium sulphate, 77-4 ; water, 21 ; impurities, 

 i '6 per cent. The crystalline form, or Se/enite, is very rarely found in these 

 marls and only lining accidental cavities. The commonest variety is 

 the saccharoidal, which is massive, brilliantly white and amorphous. The 

 more compact, transparent form of this, known as alabaster, has not been 

 found in any quantity in Notts, though worked at Chellaston over the 

 Derbyshire border. The fibrous variety consists of long narrow crystals 

 packed closely side by side obliquely to the edges of the vein or round 

 the boundaries of the saccharoidal masses. The play of light upon these 

 crystals has obtained for the variety the name of Satin Stone, under which 

 title it has been much worked at East Bridgeford for ornaments. The 

 workable variety occurs in thick nodular beds or floors, in large spheroidal 

 or lenticular masses called balls or bowls, or in rows of cakes. 1 In places 

 where any large lump occurs the stratification of the surrounding marls 

 is disturbed on all sides as though irregularly pushed out by the growth 

 of the lump. This has suggested that the mineral was originally 

 deposited in an anhydrous form as anhydrite, and that subsequent infil- 

 trations of water have caused it to swell by entering into combination to 

 produce gypsum. " This explanation is rendered more probable by the 

 occurrence of centres of anhydrite in some of the larger masses at 



1 See Metcalfe, Tram. Nott. Nat. Soc. for 1 894. 

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