Excursion to Hampstead. April 27th, 1872 - Geologists' Association excursion

From: A record of excursions made between 1860 and 1890. Edited by Thomas Vincent Holmes , F.G.S. and C. Davies Sherborn, F.G.S. London: Edward Stanford [For the Geologists’ Association], 1891. Source: Cornell University copy on the Internet Archive (Public domain work)

Figure 60 Section from Pinner to Hampstead (1 inch to 2 miles) By J.L. Lobley.

Figure 61 The Mount, Ealing. Excavation of the south side, October 1882.

Figure 62 Section at the Mount, Ealing.

Directors: S. R. Pattison, F.G.S., and Caleb Evans, F.G.S. (Report by Caleb Evans.) (Proc. Vol. iii. p. 67)

[The Association visited Hampstead for the first time on June 11th, 1870, when the collection of the late Mr. Caleb Evans was also inspected. A brief report appears Proc. vol. ii. p. 14.]

The party assembled at the Swiss Cottage Railway Station.

On reaching the fields by the shaft of the Midland Railway tunnel near Belsize Lane, Mr. Pattison explained that the lower parts of the district consisted of London Clay, and that the upper part of the hill was composed of sand, which was an outlier of the lower part of the Bagshot Sands. This porous sand acted as a kind of sponge and the water which percolated through it, being upheld by the impervious London Clay below, appeared as springs on the sides of the hill. These springs served as a good indication of the junction of the two formations.

No animal remains (with the exception of a few casts of shells and some rare indications of fishes) have been obtained from the Bagshot Sand in the London Tertiary area, but in Sussex the Bracklesham Beds—the equivalent of a part of these sands—contain a very varied fauna, which is perhaps only exceeded in richness by that of the Calcaire grossier of the Paris Basin, a deposit of probably the same age. Equivalent strata are also seen at the Hill of Cassel in the north of France, from which spot Mr. Pattison had obtained Cerithium giganteum of large size.

Mr. Evans then, with the aid of sections and a large geological map of Hampstead, explained the geology of the district, and stated that the stiff London Clay passed in its upper part into a sandy clay which formed the hill at a definite level. Fossils were very abundant in this sandy clay, especially Pectunculus decussatus and Valuta nodosa. These shells had been obtained from the spot where the visitors were then assembled, the lower part of this stratum having been traversed in the shaft of the Midland tunnel.

The party then proceeded to the Conduit Spring, which indicated the presence of the Bagshot Sand, and by the aid of an aneroid barometer it was shown that the "Pectunculus-bed" was about 50 feet in thickness.

The drains in course of construction in the Greenhill Road exposed a good section of the sands; and the party then followed, as nearly as possible, the line of junction of the sand and clay, which was indicated by pools of water in Gayton Road, by the chalybeate spring in Well Walk, and by the springs near the pond in the Vale of Health.

The character of the valleys, which were observed to radiate from the central plateau of sand, was noticed, and the party ascended to the higher ground and examined the sand there exposed in pits.

In the large sand-pit on the top of Hampstead Heath, opened a few years since for the purposes of the Midland Railway, attention was particularly directed to the gullies or small ravines which had been excavated since that time by the action of the rains falling on the surface and percolating through the. porous deposit until checked by the thin bands of sandy clay which are interstratified with the sands. It was suggested that these ravines furnished an illustration of the process by which the diverging valleys around Hampstead had been formed. It was also suggested that the flint pebbles, scattered over the surface of the heath, might be the remains of higher strata, which had been removed by the gentle but powerful action of subaerial denudation.

From the Mound, near North End, the geological character of the country to the north was explained. The high range of hills by Bushey and Elstree forms the northern escarpment of the London Clay, and the intervening range of hills by Hendon and Finchley is capped by Glacial clays and gravels resting on an eroded surface of the London Clay.

On the West Heath the position of the junction of the Bagshot Sand and the London Clay was again seen, and the spot by the Leg of Mutton Pond, where Pectunculus decussatu &c., had been obtained during drainage excavations, was pointed out.

In order to afford the members an opportunity of observing the effect produced on the surface by the superposition of the water-bearing sand above the London Clay, they were then conducted across the swamp which occurs in the lower parts of the West Heath Valley.

[The next excursion to Hampstead took place on June 22nd, 1874, Caleb Evans again being Director. There is a very brief report of it in Proc. vol. iv. p. 155. Mr. Evans also conducted another party of the Association to Hampstead on June 16th, 1877, from the report of which the following details are taken. (Proc. vol. v. p. I60.)]

The absence of any clear sections of the Lower Bagshot Sand or of the London Clay obliged the party to confine their attention chiefly to the geological structure of the surrounding district, and having proceeded to the top of the hill by the flagstaff; the positions were pointed out of Harrow-on-the-Hill with its small outliers of Bagshot Sand, of the high ridges above Stanmore, Elstree, Highwood Hill and Mill Hill capped with patches of Pebble-gravel of doubtful age, and of the intervening district around Hendon and Finchley, on which Glacial deposits yet remain. From the neighbourhood of North End the difference was noted between the prospect to the northward, where the district occupied by the Glacial deposits presents the appearance of a wide and level plateau as far as the eye can reach, and the view to the northwest of Hampstead, where the country is composed of London Clay with small cappings of sand or gravel; and is more diversified by detached hills and intervening valleys. In the immediate neighbourhood of the heath the diverging valleys occupied by the Hampstead and Highgate ponds, forming the headwaters of the Fleet river, were noticed, as probably resulting from the outflow of springs at the junction of the London Clay with the Bagshot Sands. Examples of these springs were well seen at the Vale of Health and at Well Walk, and after tasting the chalybeate water at the latter spot, the party proceeded to the residence of the Mr. Evans, and examined his collection of Tertiary fossils, many of which were obtained by him in the neighbourhood of Hampstead.

[An excursion to the Brent Valley and Hampstead took place on May 7th, 1887, J. Logan Lobley being Director. An account of it may be read in the Proceedings, vol. x. p. 148. In the same part may also be seen the report of an excursion to The Mount, Ealing, and Horsington Hill, on June 18th, 1887, J. Allen Brown, Director.]

Maps

Ordnance Survey. Geological. Sheet 7. (Drift.) 8s. 6d.

New Ordnance Survey. Sheet 256. 1s.

Stanford's Geological Map of London. 5s.

Books

W. Whitaker, Geology of London, 2 vols, 8vo, London (Geol. Surv.). 1889. 11s.

W: Whitaker, Guide to the Geology of London, 8vo, London (Geol. Surv.), ed. 5. 1889. 1s.

C. Evans, On the Geology of Hampstead, Proc. Geol. Assoc., vol. iii. pp. 29-32, map.

J. L. Lobley, Hampstead Hill, 4to, London. 1890.

J. L. Lobley, The Geology of the Parish of Hampstead,

Trans. Middlesex Nat. Hist. Soc., 1886-7, pp. 64-102.