1878.] 
Superficial Gravels and Clays. 
319 
the line of section, the chalky boulder-clay is exposed in 
patches overlying coarse gravel, and that again a sandy 
gravel. Further up the line this sandy gravel is super- 
imposed upon a dark blue clay with much liassic detritus. 
When the cutting was being made Mr. Walker traced this 
blue clay for a distance of a mile and a half towards East 
End, considerably past my line of section. A little south- 
west of the railway the line of section crosses the top of the 
watershed between the Lea and the Brent. Descending the 
slope I was so fortunate as to find a large excavation for 
obtaining gravel and sand in the grounds of the Avenue, and 
the following section exposed : — 
Section at the point marked d in Fig. i 
s. Surface soil. A, 1. Chalky boulder-clay. A, 2. Coarse gravel. Pebbles mostly 
rounded. c. Very sandy gravel. Mostly sand at top; coarser towards bottom 
of sedtion. Base of gravel not seen. 
The upper part of the clay, both here and at Mr. Plow- 
man's clay-pit, is brown and without chalk. 
The line of sedtion crosses a small valley running into 
the Brent, and, after passing the Finchley Road, reaches 
Mr. Lawford’s brick-field at Church End. The beds exposed 
in this pit are shown in Fig. 5. 
In this sedtion the Upper Boulder-clay is much thinner 
than higher up the hill, and contains very few stones ex- 
cepting in nests next the surface. These surface patches of 
pebbles mark the extent to which the clay has been subjedted 
to subaerial denudation, the finer materials having been 
carried away and the coarser left behind. This denudation 
has been greater on the slopes than on the plateaux, so that 
it is on the latter that we find the clay now thickest. 
