A HISTORY OF NOTTINGHAMSHIRE 



THE JURASSIC SYSTEM 



The beds which succeed the Keuper Marls in the east and south 

 borders of the county could scarcely be more contrasted with them 

 either in nature or contents. Any line to be drawn between two 

 systems on local grounds must be drawn here. Opinions have been 

 always more or less divided, according to the locality in which they are 

 studied, 1 as to the position of these upper strata, whether they should be 

 placed in the Jurassic or Triassic systems. Here that question decides 

 itself in favour of the Jurassic. Although, however, these beds belong 

 to the same system as the Lias above them they are distinct from it and 

 are named Rhastic. 



The RH^TIC formation here commences with Black Shales, which 

 rest with a sharp line of demarcation on the tea-green Marls of the 

 Keuper. These tea-green Marls were at one time taken as the base of 

 the Rhastic, but they are now believed to be merely discoloured by the 

 deoxidation of the red colouring matter through the decay of pyrites in 

 the overlying beds. The Black Shales are ' thinly laminated and contain 

 a few thin bands of sandstone and a bone bed at or near the base.' They 

 have also been called Contorta-beds from the abundance in them of the 

 shell Cassianella contorta. Above these come a series of ' thick bedded 

 light- coloured marls with yellowish fine grained limestone in irregular 

 nodular bands ' (Geol. Survey) often called White Lias. Each of these two 

 groups is about 15-20 feet thick. The Black Shales are not strong 

 enough to make much show on their outcrop, but the hard slabs of the 

 White Lias with Pleuromya croisocombeia on their surface make a slight 

 scarp in the neighbourhood of Elton and Barnston. 



The characters of both groups are best seen in artificial openings. 

 At Beacon Hill, Newark, 1 9 feet of Black Shales are seen with Cassianella 

 contorta and ' Pullastra arenico/a,' but neither sandstone nor bone bed has 

 been seen in situ the latter has probably decayed. The upper group 

 has only been reached by excavating through the Lias to prove its 

 presence. At Elton is seen a bone bed overlain by black paper-shales 

 and at the station the upper group. At Kelvington cutting 18 feet of 

 the upper group containing Estheria minuta overlay the shales. At 

 Gotham cutting both groups, the lower 15 feet and the upper 18 feet 

 thick, were found, but no bone bed. Near this spot is the Orston ' spa,' 

 supposed to be mineralized by the decay of pyrites from the bone bed. 

 At Barnston the lower group is 1415 feet thick, and contains a pyritous 

 bone bed with vertebrate remains, and the upper group is 18 feet thick. 

 In the Midland Railway cutting at Stanton-on-the-Wold 13 feet of the 

 lower group were seen, including two narrow pyritous bands and Cassian- 

 ella contorta^ Schizodus e/ongafus, Protocardium rhceticum and Modiola minima 

 in the upper part and a coprolitic bone bed in the lower part, with spines, 

 scales, teeth and bones of the following : 



1 See Renevier, Alpes Vaudoises, InfraSas, 1864. 

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