Chalk Marl 



29 



Chalk Marl. The eastern pit is topped by some six to twelve 

 feet of river gravel containing mammalian bones. This will 

 be described later. It rests on a firm but irregular surface of 

 the lower Chalk Marl, here quite yellow in colour. Fossils are 

 not abundant in the marl but Terebratida semiglobosa, Ostrea 

 vesicularis, Lima, and Inoceramus may generally be picked up. 

 The Greensand bed below is typically rich in fossils but is now 

 no longer washed. Its commonest fossils are sharks' teeth, 

 Avicida gryphaeoides, Plicatulasigillina, Terebratula biplicata, 

 Terebratidina triangular is, Belemnites minimus, Ammonites 

 rostratus and A. splendens. Most of these occur both as 

 pebbles and as contemporaneous fossils, but the ammonites 

 are all derived. The Gault below is exposed for about thirty 

 feet ; it is quite normal in its character and, as above 

 mentioned, contains numerous lamellibranchs. 



Another interesting exposure is that of the Mill Road 

 Cement Works, Cambridge. There the Greensand is taken 

 out as exposed and, when sufficient accumulates, is washed 

 for its coprolites. At certain times good material can be 

 collected as of old. Gasteropods are the speciality of the 

 locality and the crabs Eucorystes and Palaeocorystes are not 

 rare. The Greensand is overlain by some twenty feet of marl. 

 At Hauxton Mill is another very similar pit which, in times 

 past, has yielded many fine fossils. The Chalk Marl is here 

 more fossiliferous than usual and yields Kingena lima and 

 occasional casts of ammonites. 



Of othe? exposures we may note those of the cement works 

 on both sides of the Great Northern Railway, near Shepreth 

 station and to the east of it. Also the various pits at Meldreth, 

 Bassingbourne, Orwell, and Madingley, but none of these 

 exhibit complete sections or show the relationship of the beds 

 to their surroundings. 



Chalk Marl disturbed by the extraction of the coprolite 

 bed at its base may also be seen in all the above-mentioned 

 brickyards of the Gault. 



