148 Mr. Williamson on the Distribution of 



my own observations extend, the following fossils appear to be confined to it in 

 Yorkshire : 



Gryphaea dilatata, var. /3. 

 Turbo sulcostomus. 

 Trochus guttatus. 



Cirrus depressus. 



Belemnites tornatilis. 



Nautilus hexagonus? (see page 149, line 11.) 



The last fossil has, I believe, been met with in another stratum, in the South 

 of England. The palatal tooth of a fish apparently belongs to the genus Orodus 

 or Psammodus (Agassiz), and closely resembles teeth from the forest marble. The 

 Saurian remains chiefly consist of detached vertebrse of the Ichthyosaurus. In one 

 instance I met with a large coracoid bone ; and a fine humerus of a Plesiosaurus 

 was found at Hackness. 



In Gristhorpe Bay the Kelloways rock is less arenaceous and ferruginous, and 

 is sometimes slightly calcareous. The hard ironstone forming the top of the stra- 

 tum at Scarborough is wanting at Hackness, its place being occupied by a blue clay 

 containing numerous fossils, of which Ammonites Jlexicostatus is the most abun- 

 dant. The lower part of the stratum is a fine-grained arenaceous rock, very soft 

 when first removed from the quarry, but hardening rapidly on exposure to the 

 atmosphere. It forms one of the finest building-stones in the east of Yorkshire, 

 on account of the uniformity of its colour, its durability, or the ease with which 

 it is worked. It appears to contain a greater abundance of Ammonites sublavis 

 and A. Sutherlanders than at Scarborough. The thickness of this stratum varies 

 considerably, being in some parts much greater, and in others less than thirty-five 

 feet, the dimensions which it attains at Hackness. North of Scarborough Castle 

 it is from sixty to seventy feet. 



Oxford Clay. 



Reposing on the Kelloways rock is the Oxford clay, generally averaging about 

 130 feet in thickness. It is not separable into divisions, consequently the task 

 of directing the collector to the sites of its fossils becomes more difficult. The 

 lower part of the formation is of a dark blue colour, argillaceous, and splits freely 

 into small laminae, or rather rhomboidal fragments. As we ascend in the section 

 it gradually loses its argillaceous character, becoming more arenaceous, and is 

 slightly tinged with yellow as it approaches the calcareous grit. 



Organic remains are comparatively rare in the Oxford clay of Yorkshire, owing 

 partly perhaps to so limited a portion of it being exposed to the action of the sea 

 on the coast, whilst inland it is not laid open by pits. With one exception, the 

 fossils seem to occur in the lower part of the formation ; and the portion imme- 

 diately reposing upon the Kelloways rock seems to be characterized by the pre- 



