• 86 



From the frequency of the words "gravel pit" on the 

 Ordnance Map between Great Gransden and Eltisley, it might 

 be supposed that there was here an extensive area of Glacial 

 gravel ; this however is not the case, Boulder Clay can be seen 

 in the immediate neighbourhood, and the pits themselves 

 appear to liave been dug in small hollows or pot-holes of denu- 

 dational gravel resting on the Clay. 



It may be mentioned that in the valley at Caxton End near 

 Bourne the Neocomian Sands come up to the surface, probably 

 forming a ridge against which the Boulder Clay thins out, for it 

 is found filling up the valley lower down. Mr S. V. Wood, 

 Junr. notices a similar disposition of the Boulder Clay near 

 Gamlingay (see ante p. 17), speaking of this deposit as bedded 

 round the Lower Cretaceous Sand, the two sections however 

 which he gives across this district are inaccurate in several 

 particulars. In the first place he ignores the existence of the 

 Gault upon which the Boulder Clay rests about Wrestlingwortli 

 and Tadlow, and which crops out in the valley east of Potton ; 

 it is evident moreover from the lie of the formations that it also 

 rests upon Gault at the Old North Road Station, and that the 

 latter must have formed a great part (at least 60 ft.) of the 

 mass pierced by the well and called Boulder Clay by Mr S. Y. 

 Wood. The Glacial Clay merely appears to have filled up a 

 pre-existent valley, and there is no evidence of any great scoop- 

 ing out of the Gault as Mr Wood supposes ; there can I think 

 be little doubt that the water was obtained from the Neocomian 

 Sands, for there is no evidence of any Middle Drift in the neigh- 

 bourhood ; the gravel near Moggerhanger also is probably of 

 later date than the Boulder Clay. I would therefore correct 

 the section given by Mr Wood as follows ; the minor details of 

 the geology being of course omitted on so small a scale. 



Fig. 1. Diagram Section from Old North Eoad to the Ouse Valley. 



W.S.W. 



Horizontal scale 4 miles to an inch; Ycrtical, one inch = 300 feet. 

 = Jurassic Clay. r = Gault. ;r-= Post-glacial Gravel. 



-Neocomian Sands. / = Boulder Clay. 



