Fig. 6.
[Fig. 6] is a general or average section of the strata on which London stands. The increase in the proportion of the argillaceous strata, and the decrease of the beds of sand, in the Lower Tertiary strata is here very apparent, and from this point westward to Hungerford, clays decidedly predominate; while at the same time the series presents such rapid variations, even on the same level and at short distances, that no two sections are alike. On the southern boundary of the Tertiary district, from Croydon to Leatherhead, the sands 3 maintain a thickness of 20 to 40 feet, whilst the associated beds of clay are of inferior importance. We will take another section, Fig. 7, representing the usual features of the deposit in the northern part of the Tertiary district. It is from a cutting at a brickfield west of the small village of Hedgerley, 6 miles northward of Windsor.
Fig. 7.
Here we see a large development of the mottled clays, and but little sand. A somewhat similar section is exhibited at Oak End, near Chalfont St. Giles. But to show how rapidly this series changes its character, the section of a pit only a third of a mile westward of the one at Hedgerley is given in [Fig. 8].
