AND LOAMS OF WEST HKUTS, 



ir.i 



cemcntins;' material, fi'lspar-]Kirp]iyry, lydian-stonc, chrysoprasc, and 

 pseudoiuorplis of limoiiito after jasper, arc also met with. The 

 finest portion, or matrix, consisting of grains less than three- 

 sixteenths of an inch in diameter, is mainly composed of angular 

 and subangular pieces of flint and quartz, rounded (quartz-pebbles, 

 and pieces of limouite. Of course the composition of the gi'avels 

 varies considerably, and constituents which form a very marked 

 feature at one locality may be present only in small quantity at 

 another ; thus the presence of numerous largo quartzite- and <][uartz- 

 pebbles is a marked feature in the lower parts of the gravel near 

 the sonthern end of the Watford Tunnels, and some of the gravels 

 near Bushey are chai'acterized by the presence of a large number of 

 well-rounded flint-pebbles. The number of these pebbles, derived 

 from the Tertiary beds, usually increases considerably as the 

 Tertiary escarpment is approached. 



The beds of gravel are often associated with beds of loam, 

 clean and often well-washed sand, and occasionally with very 

 small locally-developed layers of blue clay, which is very similar 

 in appearance to boulder-clay. The general character of the 

 deposits is shown in Sections 1, 2, 7, and 8, taken in the Watford, 

 Aldenham, and St. Albans districts. In all these cases an irregular 

 but decided stratification is clearly shown, indicating that the 

 beds were deposited from running water. 



Section 8. — Bernakd's Heath, St. Albans. 



A. Soil. 



B . Gravel with many flint pebbles. 

 b. Tliin bands of manganese oxide. 



C. Manganese bed. 



D. Variegated sands. 



E. "White sand. 



F. Clay with flint pebbles. 



G. Brown and green loams. 



H. Brown clay -with -flints. 

 I. Chalk. 



fcc 

 ■■B 



p=; 



Before concluding this description of the composition of the 

 beds, an account will be given of some thin and locally-developed 

 beds of exceptional character. Some of these are shown in 

 Sections 1, 2, 7, 8, and 10, from the Watford and St. Albans 

 districts. These deposits, which I have marked on the sections as 

 the " manganese beds," are usually black in colour, and are better 



