18G8.] JUDD SPEETON CLAY. 249 



Myadte. — Pioiopcea plicata, Sow., sp., and F. Neocomiensls, Desh., 

 sp., both occur in the Speeton Clay, the latter being very abundant 

 throughout the Neoconiian beds. 



Pholadomya Martini, Forbes. — Remarkably fine specimens of this- 

 shell occur both in the Upper and Middle Neocomian of Speeton. 



Thracia PhiUipsii, Rom., occurs in the Middle and Lower Ncoco- 

 mian, while a more elongated species or variety is found in the upper 

 beds. 



Thetis Sowerhyi, Rom. — Both the varieties of this shell, so 

 abundant in, and characteristic of, the Lower Greensand, are found 

 in the " Cement-beds " at Speeton. 



Toxaster complanatus, Ag. sp. — Of this most highly characteristic 

 Neocomian fossil the only known specimen from the Speeton Clay 

 is in the Scarborough Museum. This fossil was identified by Agassiz 

 himself in 1838. Its rarity, like that of all the more delicate fossils, 

 is accounted for by the large quantity of easily decomposing pyrites 

 which the lowest Neocomian beds at Speeton contain. This species, 

 which is so very abundant in the Neocomian limestone, has received 

 a great number of names, among which are Holaster com.planatusy 

 Ag., Spatangus retusus, Lam., S. helveticus, Defr., and S. argillaceus, 

 PhiU. 



A Cidaris, with beautiful muricated spines like some of the French 

 Neocomian forms, and a Pseudodiadema, with smooth spines, occur 

 in the " Cement-beds " at Speeton. 



Pentacrinus angidatus, Rom., and P. Fittoni ? occur in the upper 

 and the middle beds of the Speeton Neocomian. 



Appendix C. — On the Economic Products of the Speeton Clay. 



The Speeton Clay is not altogether without interest in a commer- 

 cial point of view. For the last thirty years past the inhabitants of 

 the neighbouring villages have been in the habit of digging at the 

 surface of the cliff the large septaria of the " Cement-bed ;" these, 

 as they were accumulated in sufficient quantities, were transported 

 from time to time to Hull by coasting vessels. But during the last 

 five or six years the cliff has been leased from the lord of the manor, 

 and the " cement-stones " have been found so valuable as to induce 

 the undertaking of regular mining-operations. The mode of work- 

 ing is as follows : — Timbered adits are driven into the cliff at points 

 below the outcrop of the " Cement-bed ;" it has already been shown 

 that the beds of the Speeton clay dip inland at a considerable angle, 

 consequently these adits sooner or later meet the Cement-bed ; when 

 this occurs, galleries are driven in every direction in the bed itself, 

 the material and refuse b^ing carried out in small waggons run- 

 ning on tramways which are laid down in the adits. The stone is 

 now usually conveyed to Hull by railway. 



The peculiar, light-coloured, fine-grained, argillaceous limestone of 

 the Speeton septaria is manufactured into Roman cement, for which 

 purpose it is very highly prized. The cement made from it is said 

 to be particularly valuable, on account of the rapidity with which 

 it sets and from its not being liable to crack in drying. In these 



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