Gault 



25 



that the Upper, and in places, the higher part of the Lower 

 Gault has been used up in the process and is therefore absent 

 in the "district. 



The Gault of Cambridge is a stiff tenacious clay, dull 

 leaden grey in colour and with a tinge of brown in it. On 

 drying it becomes much paler but still retains the same dead 

 hue. It varies little from bed to bed and contains many 

 indigenous phosphate nodules sporadically distributed. It is 

 generally rather unfossiliferous, but certain of its beds are by 

 no means so, and occasional Plicatulae and Belemnites can be 

 picked up from most of its exposures. 



The lower part of the Cambridge Gault is never well 

 exposed. Most of its outcrop is covered by drift and has 

 never yet been exploited for brick-making. At Upware it is 

 occasionally dug on the river side of the South pit for use 

 in bank making, and in these circumstances the lowest layers 

 may be easily seen. The Gault here rests directly on Lower 

 Greensand and appears to overlap it on to the old coral reef. 

 Its lowest layers are glauconitic and somewhat sandy in 

 texture. Belemnites attenuatus and B. minimus abound, and 

 the nodules of a phosphate bed, about a foot from the base, 

 consist largely of Ammonites interrupts \ Nucula and Inocera- 

 mus sulcatus are also plentiful. 



Similar fossiliferous beds are found all over the county 

 at the base of the Gault, and well-sinkers accordingly hail 

 with joy the appearance of fossils in their diggings. 



The higher part of the Cambridge Gault is well exposed 

 and can be examined at leisure in the fine sections provided 

 by the brickyards of Barnwell, and also at Barrington. Less 

 interesting exposures are open about a mile from Cambridge 

 along the Barton B/oad, on the Ely Boad, at Clayhithe, and at 

 Soham. The upper surface is often bared in coprolite workings 

 and in many places where the Chalk Marl is being worked for 

 cement. 



Derived and somewhat worn fossils from the Upper Gault 

 are extremely abundant in the Cambridge Greensand, and the 



