42 The Geology of Cambridgeshire 



The only place in Cambridgeshire where Boulder-clay is 

 worked for economic purposes is the brickyard between Long 

 Stanton and Over, where a very dark fine-grained and almost 

 laminated clay with Jurassic fossils and striated chalk boulders 

 is made into bricks. The more usual exposures are ponds, wells, 

 ditches, cemeteries, building excavations, and occasional road 

 or railway cuttings. These last furnish the best exposures, 

 but as the Boulder-clay is absent from the steeper slopes and 

 occurs only high on the hills or deep in the valleys few 

 cuttings are available, and these all where the railways cross 

 watersheds, as between Bartlow and Haverhill, and about Old 

 North Road station. A good road section is seen at Hadstock 

 village. Small streams running over impervious Boulder-clay 

 sometimes provide exposures, as about Kingston and Bourn, 

 and chalk or clay pits worked in the underlying solid rock 

 may also have a little Boulder-clay as at Ely, Shudy Camps, 

 and Chesterford. 



(b) Plateau Gravels. 



Above the Boulder-clay of the Chalk Escarpment are the 

 curious accumulations of rudely stratified material to which 

 the name Plateau Gravels is often given. 



The Plateau Gravels consist, in the main, of the same 

 materials as does the local Boulder-clay, but contain a far 

 smaller proportion of chalky material. Their pebbles are 

 practically unworn and often retain the striae so characteristic 

 of the boulders in the Boulder-clay, and, in fact, the whole 

 aspect of the ' gravel ' is that of the less soluble residue of the 

 local Boulder-clay. No indigenous fossils have ever been dis- 

 covered among the 'gravels,' and the re-sorting of the materials 

 has been most imperfectly carried out. Plateau Gravels seem 

 only to occur where the Boulder-clay is exceedingly chalky 

 and are unknown in the clay districts of the west. They 

 sometimes appear to overlap the present Boulder-clay and 

 rest directly on the Chalk. The most accessible exposures are 

 the higher hill slopes of the spur which joins Barrington Hill, 



