PRESTWICH WOOLWICH AND READING SERIES. 91 



ones, less than half a mile apart. In this short distance the mottled 

 clays almost entirely disappear and are replaced by sands*. 



At Uxbridge and Pinner the mottled clays are largely developed. 

 The shafts sunk to procure chalk at the latter place f give sections 

 very similar to that at Hedgerley ; but on Pinner Hill, in place of 

 the mottled clays, sands and pebbles predominate, as shown on the 

 side of the lane leading from the summit of the hill to Hamper Mill. 

 At Watford a remarkable development of the rolled pebble bed im- 

 mediately overlying the chalk occurs. It there forms a mass 15 feet 

 thick, with a matrix of ochreous clayey sand, which gives it the ap- 

 pearance of the ordinary drift-gravel. 



Fig. 5. — Watford {general section on railway, Bushey cutting). 

 3 ^^ 



id 



3. London Clay. Feet. 

 I. Basement-bed of the London Clay with numerous fossils 5 



(d. Sands 3? 

 c. Mottled clays with a few beds of sand 35? 

 b. Sand nearly white, with a few layers and patches of flint-pebbles ... 10 

 a. Shingle-bed of flint-pebbles in ochreous sand 15 



68 



4. Chalk 5 



At Welwyn this division consists essentially of sands with irregular 

 subordinate beds of grey clays, occasionally mottled red and green, 

 layers of flint-pebbles, and thin seams of iron-sandstone. At Hatfield | 

 the mottled clays are entirely replaced by sands, which at Hertford 

 again give way in part to clays. The oyster bed overlying the chalk 

 is developed again in this neighbourhood. The sections are from 

 pits in a brick-field at George's farm, one mile from Hertford, on the 

 London road. 



* For a section of the Hedgerley Pit (10) see Journ. Geol. Soc. vol. vi. p. 268. 

 t A section in full, taken by Mr. Morris, of the Pinner pits is given in Journ. 

 Geol. Soc. vol. vi. p. 269. 

 X For the section at this place see Quart. Journ. Geol. Soc. vol. vi. p. 270. 



