II. THE SUPERFICIAL GRAVELS AND CLAYS

AROUND

FINCHLEY, EALING, AND BRENTFORD.

By THOMAS BELT, F.G.S.

I. Introduction.

PURPOSE in the present paper to show the relation of the Glacial-beds at Finchley to the implementbearing gravels at Ealing, and the mammaliferous gravels and sands at Brentford.

Possibly the objects I have in view-to demonstrate that the formation of the valley-deposits took place in the Glacial period, and that palæolithic man was pre-diluvial-might have been more clearly attained by a thorough study of one of the more northern valleys; but I have had much greater facilities for making myself acquainted with the district I have chosen. It has also this great advantage, that it is close to London, so that my descriptions and conclusions may be readily checked by an inspection of the numerous gravel and clay-pits from which I have obtained the facts. described in these pages.

II. Description of the Deposits.

1. Finchley and Neighbourhood.-The Glacial beds in the neighbourhood of Finchley were described in 1835 by Mr. Edward Spencer,* who traced the boulder-clay and underlying gravels from Muswell Hill to Finchley Common. Mr. Whitaker has mentioned them in his "Memoir on the Geology of Parts of Middlesex, &c.,"+ and Mr. Henry Walker has described the beds exposed in the cuttings of the Great Northern Railway and the clay-pits in the vicinity.‡

My own observations date from July, 1875, when I first visited the clay-pits near Finchley under the guidance of Mr. J. J. B. Ives. Since that time I have neglected no opportunity of examining the numerous sections that have been exposed in excavations for the foundations of new

*Proc. Geol. Soc., vol. ii., p. 181.

+ Mem. Geol. Survey, 1864.

Proc. Geol. Assoc., vol. ii., p. 289, 1871.

FIG. 2.-SECTION FROM ARGYLE ROAD, CASTLEHILL TO SOUTHALL.

Scale as above. a. Brick clays.

b. Sands and gravels.

houses, as well as the more permanent ones in the graveland clay-pits. In this way I have been able to trace the beds right across from the drainage area of the River Lea into and across that of the Brent.

The general distribution of the deposits is shown in Fig. 1, which is a section extending from a little east of the "Green Man" public-house, on the St. Alban's Road, to the top of the hill at Hendon. The following are the details from which this section has been constructed :

At an old brick-pit at the eastern extremity of my section the Upper Boulder-clay has been worked, but the surface is now grassed over. Lower down the slope I found a gravelpit open about 250 yards directly west of the "Green Man" public-house, on the south bank of a small stream running to the Lea, and obtained the section shown in Fig. 3.

GRAVEL-PIT NEAR EASTERN END OF GENERAL SECTION.

s. Surface soil. A. Brown boulder-clay, unstratified, with bluish vertical partings. Stones mostly flints, with a few pieces of quartzite, sandstone, chalk, &c., the chalk mostly decomposed. c. Sands and gravel. Mostly sand at top, with lines of small gravel. Sandy coarse gravel below. Pebbles mostly subangular. Base

not seen.

In this section the chalk has been mostly dissolved out of the clay, but pieces, generally quite soft, are still to be found in places, and in others the calcareous matter has entirely disappeared, leaving behind, nests of siliceous grains originally contained in the chalk. Ascending the hill westward, a good section of the boulder-clay is exposed in Mr. Plowman's brick-field. The clay here contains much chalk detritus and many other travelled stones, including pieces of granite, lias, and red chalk. Just beyond this is the cutting of the Great Northern Railway. The slopes are now mostly grassed over, but the beds were examined and described by Mr. Henry Walker when the section was well exposed. He found a chalky boulder-clay overlying a blue boulder-clay, with occasional patches of sandy gravel between them. At Finchley Station, about 550 yards to the north-west of

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 superimposed 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 southwest 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 :

s. Surface soil.

rounded.
of section.

SECTION AT THE POINT MARKED d IN FIG. I.

A, 1. Chalky boulder-clay.

A, 2. Coarse gravel. Pebbles mostly c. Very sandy gravel. Mostly sand at top; coarser towards bottom Base of gravel not seen.

The upper part of the clay, both here and at Mr. Plowman's clay-pit, is brown and without chalk.

The line of section crosses a small valley running into the Brent, and, after passing the Finchley Road, reaches Mr. Lawford's brick-fleld at Church End. The beds exposed in this pit are shown in Fig. 5.

In this section the Upper Boulder-clay is much thinner than higher up the hill, and contains very few stones excepting in nests next the surface. These surface patches of pebbles mark the extent to which the clay has been subjected to subaërial 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.

The patches of gravel marked 2 in Fig. 5 are very irregular. Some of them look like lumps of the Middle Sands and Gravel that had been picked up and deposited in a

SECTION AT MR. LAWFORD'S CLAY-PIT, CHURCH END.

s. Surface soil. A, I. Brown boulder-clay with few stones, excepting in nests near the surface. A, 2. Irregular patches of sandy gravel. A. 3. Alternations of

laminated clay, sandy clay, and sand, with some lines of fine gravel. c. Sandy subangular gravel, with rounded quartz pebbles.

frozen state, the originally horizontal stratification having in their new position been turned on end.

The line of section now crosses to Hendon Lane, where many gravel-pits have been opened, but most of them are

Brown boulder-clay, with few stones. A, 2. Irregular patches of gravel.

3. Laminated dark sandy clay.
London Clay

c. False bedded sands and small gravel.

now filled and houses built over them. In July, last year, I visited the spot, in the company of Mr. Henry Hicks, and obtained the section shown in Fig. 6, a little to the north of the line of the general section.