Oxford Clay 11 



JURASSIC. 



Oxfvrdian. 



The oldest rocks of Cambridgeshire belong to that division 

 of the Upper Oolites which is known as the Oxford Clay. 

 This clay covers a very considerable area in the north and 

 west of the county, but much of the tract which it occupies is 

 drift-covered, and artificial exposures are rare. The total 

 thickness of the Oxford Clay hereabouts has been variously 

 estimated at from 400 to 600 ft. A well was sunk at Blun- 

 tisham to 300 ft., but did not reach the base of the deposit. 



The lower beds may be seen about Peterborough, in the 

 adjoining county. The Belemnites Owenii beds are there 

 extensively worked for bricks, and a number of reptilian bones 

 and Ganoid fish, as well as Belemnites and other Mollusca, 

 have been obtained from them. 



At Whittlesea, in Cambridgeshire, there are large brick 

 works in similar beds, which possibly appertain to a higher 

 horizon. 



In the more accessible pits of Huntingdonshire and Bed- 

 fordshire much higher beds are worked, and the resulting 

 bricks are white or yellow instead of red. 



At Eynesbury, near St Neots, in Huntingdonshire, the 

 beds with the ornatus group of ammonites are well exposed : 

 they are grey or grey-blue clays, which on weathering become 

 creamy. They are underlain by much darker clays, which 

 weather brown, but these are apparently not so profitable to 

 work and are badly exposed. Thin bands of marly or sandy 

 limestone occur at intervals through the clay, and it is from 

 these or from associated beds that the best preserved am- 

 monites are obtained. One bed recently exposed was a mass 

 of Ammonites at/ileta, the individuals ranging up to a foot 

 and a half across. 



Sandy (Bedfordshire) is another well-known locality for 

 fossils. Here, a little beyond the station, higher beds are worked, 



