]04 THE LIAS AMMONITES. 



vol. 1862. " Zone des Am. spinatus" Schlonbach, 'Eisenstein des mittl. Lias./ p. 489, 

 1863. " Schicliten des Jm. S2nnatus," Emerson, ' Die Liasmulde von Markoldendorf/ 

 p. 35, 1S70. "Zone aPeden cequivalvis" (pars sup.), Dumortier, ' Etudes Pal. Bassin 

 du Rhone,' torn, iii, p. 213, 1869. " Marlstone Rock-bed " (pars), Judd, " Mem. on the 

 Gaol, of Rutland," 'Mem. of Geol. Survey,' 1875. "Zone oi Am. spinatus," Tate and 

 Blake, 'Yorkshire Lias,' p. 118, 1876. "The spinatus zone," Rev. Dr. Ered. Smithe, 

 * Trans. Cotteswold Nat. Club for 1876,' p. 349. 



The bed with Amaltheus spinatus is so closely united with the zone of Amal. margaritatus 

 that it appears to form the upper part of the Marlstone Rock-bed in the Midland Counties. 

 It in general consists of a hght-coloured, friable, sandy marlstone, containing many 

 nodules, rock fragments, and fossiliferous concretions which form inconstant bands in the 

 mass of the strata, and yield a considerable number of organic remains at Grettan, 

 Alderton, and Churchdown Hills. I have collected Amaltheus spinatus, Belemnites brevi- 

 formis, Lima Hermanni, Terehratula punctata, and Spiriferina rostrata from these nodules. 



At Down Cliff, on the coast of Dorset, the Spinatus-heds. form the uppermost portion of 

 the Micaceous Marls of De la Beche. They consist of brown sands and sandstones in 

 which Amaltheus spinatus is the characteristic Cephalopod, and with it many Gastropods 

 and other fossils ; the light-brown sands are overlain by non-fossiliferous clay, on which 

 rests a remarkable bed of Marlstone containing a great number of Gastropods, with their 

 shells in a fine state of preservation ; as the rock is very hard and ferruginous these 

 beautiful fossils are extracted with difficulty. I have collected from this bed Amaltheus 

 spinatus, Brug., Belemnites breviformis, Voltz., Pleurotomaria precatoria, Deslong. 

 p. bitorquata, Deslong., P. rustica, Deslong., P. mirabilis, Deslong., P. procera, d'Orb., 

 Cryptania expansa, Sow., StraparoUus sinister, d'Orb. ; and resting on this remarkable 

 conglomerate of well-preserved shells are beds of Upper Lias Limestone, with Harpoceras 

 serpentinum. Rein., Harp, radians. Rein., and Harp. Holandrei, d'Orb. So closely do 

 these strata repose upon the Middle Lias fauna of the Spinatus-zowQ that they all appear 

 to belong to the same bed. 



In Yorkshire the upper portion of the Middle Lias consists of argillaceous shales with 

 bands of ironstone, some of these belong to the Margaritatus, others to the 8pinatus-heAs ; 

 the workable beds of liassic ironstone are now ascertained to be found only in these 

 two horizons. The Spinatus-heds are well seen at Hawsker bottoms, where Am. spinatus = 

 Hawslcerensis, Simp., is found in beds of red ironstone doggers, the probable equivalent 

 of the Cleveland main seam, as well as in shale interstratified therewith. Another section 

 of the zone is found at Kettleness, where the beds form the base of the cHff, and at Old 

 Nab, Avhere the strata are very fossiliferous, and exhibit a fine profile of the whole. 

 The following section was carefully measured by MM. Tate and Blake,^ as it affords 

 a good type of the ironstone series of the Yorkshire coast. 



' 'Yorkshire Lias,' p. 130. 



