100 The Geology of the Railway Line from 



glauconite grains occur in it, and the tliiekness is about 8ft. Where 

 fossUs occur in the chalk rock they are very interesting, for the 

 assemblage recalls that of the chalk marl, some of the species being 

 very similar, and gasteropods common ; hence it is supposed the sea 

 became shallower at this epoch. 



That this bed must have been cut tlarough in making the line 

 near Ogboirrne Maizey is evident, because the line for some little 

 distance south of the cutting by Ogboiu-ne Maizey Bridge is ballasted 

 with it. 



The chalk rock may be seen in many pits on the high ground and 

 the marked featiu^es of the country such as those on which 

 Liddington and Barbmy Castle stand, are due to this very hard 

 bed, which has withstood denudation better than the softer chalk. 



The Upper Chalk, 



The upper chalk, next above the chalk rock, comes on in the first 

 deep cutting after lea\'ing Ogbom'ne Station. 



We fijid that flints are very numerous in the upper chalk, and 

 the layers often occur close together. These flints are so plentif id 

 that they cover the groimd, thus making a different soil to that of 

 the lower and middle chalk. 



West of Marlborough the upper chalk is very miich cut \ip by 

 valleys, and does not cover a very great area, but on the east it 

 occupies more of the ground. On the north it only begins to make 

 an appearance, and so it thickens gradually to the south, being 

 about 150ft. in thickness at Marlborough Station well, where, how- 

 ever, the higher beds are absent. 



The Marlborough Water Works well, according to information 

 supplied to me by Mr. Fairbank, the engineer, is 143ft. Gin. deep, 

 all in the upper chalk, which is not passed tlu-ough. 



The upper chalk is a most important division of the chalk for 

 many reasons. 



First, it is our great source for water-supply. The lower chalk 

 is compact and clayey, holding up rather than containing water, 

 which percolates very slowly tlu'ough it. But when it contains the 

 hai'd gritty beds seen near Chiseldon these would favom- percolation, 



