Quarterly Journal of the Geological Society of London/Volume 28/On the presence of a Raised Beach on Portsdown Hill, near Portsmouth, and on the occurrence of a Flint Implement on a high level at Downton

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1. On the presence of a Raised Beach on Portsdown Hill, near Portsmouth, and on the occurrence of a Flint Implement on a high level at Downton. By Joseph Prestwich, Esq., F.R.S. &c.. President.

A few years ago[1] I traced the well-known old beach of Brighton past Arundel to Chichester and Bourne Common—a distance of 42 miles. At Brighton it is only from 8 to 12 feet above the level of the present beach; near Arundel it attains a height of 100 feet, near Chichester possibly of 130 feet, and at Bourne Common of 140 feet. Westward of this point it had been found on the east coast of the Isle of Wight; but I failed to detect it at any point inland, or at any considerable elevation.

I now beg to call attention to an interesting section which I have more recently observed at a spot 10 miles westward of Bourne Common, and 5 miles inland. It is a mile and a half E.N.E. from Fareham, on the right-hand side of the lane leading from East Cams to Nelson's Monument, which stands on the western extremity of Portsdown Hill. This hill, as is well known, is a bare narrow chalk ridge, running 6 miles from east to west, and rising in the midst of a lower surrounding Tertiary area to a height of from 300 to 400 feet. The subangular flint-gravel of Chichester, Havant, and Portmouth ranges up to the southern foot of the hill, to a height of about 40 feet above the sea-level. It may be seen in a pit by the side of the railway half a mile west of Porchester station.

Above this lower level the slope of the hill here consists of bare chalk, with the exception of this one spot, on the north side of East Cams Wood. Although the pit is close by the road, it is not readily seen. It is situated at a height of 125 feet above the sea, or of 85 feet above the ochreous flint-gravel at its base—whence the latter stretches westward, forming the great plains of gravel extending past Havant and Southampton to Poole, which have been so well described by Mr. Codrington[2].

The pit is a shallow arc, and presents the following section:—

a. Grey earth and sand, with angular and rolled flints, 0 to 2 feet.
b. Light-coloured laminated sands, with seams of shingle,
c. Light-coloured coarse flint-shingle, with a few whole flints,
4 to 6 feet.
d. Chalk rubble, patches of.

The beds b and c constitute a true shore-shingle, composed of rolled and imperfectly rounded flints, imbedded in a matrix of light-coloured sand and loam, very different from the ochreous subangular flint-gravel at the base of the hill. In the shingle are a few Tertiary flint-pebbles, and not a few large unworn flints, with a number of sharp angular flint fragments. The only foreign material I found was a fragment of reddish quartzite. I saw no organic, remains of any description. But the pit requires further search, especially as the workmen were not present on the occasion of my visit.

I found, however, in bed a a rude flint implement; but whether derived from the surface or peculiar to bed a, I could not positively say. It was at a depth of 11/2 foot from the surface. Its type is not sufficiently distinctive to indicate its age.

I have not yet succeeded in tracing this old shingle-beach further westward, where it is desirable to determine its exact position in relation to the several gravels of the South-Hampshire area.

There can be no mistake made about the character of the shingle. It is not so rounded as the Tertiary flint-pebbles, which can be readily distinguished amongst it, while it is far more worn than the subangular gravel at the base of the hill. In places there are signs of disturbance as though from the effects of ice-action—a feature which would be in accordance with the presence of the great transported foreign boulders found in the marine gravel of Selsea, and with the chalk boulders in the Chichester sea-beach.

Fig. 1 .—Section on East side of the Valley of the Avon.
(Distance 11/2 mile.)

Quarterly Journal of the Geological Society of London, vol. 28 dec 6 no. 1 fig. 1.png


While on this subject I may mention another point of interest connected with this area, which I noticed on the same occasion. Flint implements have been found at various places, and at various elevations, in the Hampshire basin[3]—amongst others, in the valley of the Avon, near Fordingbridge, at an elevation of about 40 feet above the river[4]. Five miles north of Fordingbridge is the village of Downton. On the hill immediately east of the village is Packham Common (now enclosed); and on the right hand of the road leading from Redlinch to Standlinch Down, and passing by the north-east corner of the former common, is a small chalk-pit (see fig. 1) capped by ochreous gravel. This consists as usual of subangular flints, and a few pebbles of quartz, with some worn fragments of iron-sandstone and flint pebbles from the adjacent Tertiary strata. It reposes upon a worn and furrowed surface of the chalk, and is from 2 to 7 feet thick. A portion of this bed had slipped down; and on examining the talus for the constituent parts of the gravel I found a small flint implement, very well finished, and of the ovoid type, colour, and aspect common to those found at Waren's Pit, St. Acheul. It is 31/4 inches long by 13/4 broad, finely pointed, and white, with a porcellaneous lustre. It shows no wear. I could find no other, nor any organic remains. The elevation of the pit, according to the levels obligingly furnished me by General Sir Henry James, is about 200 feet above the river, which is here 115 feet above the sea-level.

Between this pit and the river are two other well-marked broad gravel terraces, in the lower one of which mammalian remains have been found abundantly in other parts of the Avon valley. The section is as in fig. 1.

The level of the lower terrace is from 30 to 70 feet above the river, of the second from 150 to 180 feet, and of the third or upper terrace about 200 to 250 feet.

This discovery is in keeping with that of the flint implements in the gravel of the cemetery at Salisbury, which Mr. Evans estimates at 110 feet above the river, and with those of Southampton Common, which Mr. Codrington places at an elevation of 86 and 150 feet above the river at Southampton. The difference, with the first-named of these spots especially, is that there the flint implements are of the rudest pattern and make, whereas at Downton the implement is of the neatest and best-finished construction, although the gravel is one of the oldest in the district, being prior to the excavation of the valley to the greater depth of some 200 feet, to the spread of the lower gravels, and apparently to the great development of the Postglacial mammalia.

 

Discussion.

Mr. Codrington stated that, according to the Ordnance Survey, the level of the pit at Cams Wood was not more than 100 feet above the sea, so that it was at about the same level as the gravels of Titchfield and elsewhere.

Mr. Evans remarked that the flint flake from Cams Wood presented no characters such as would prove it to be of palæolithic age. He was, on the contrary, inclined to regard it as having been derived from the surface. He commented on the height at which the Downton implement had been discovered, which was, however, not so great but that the containing gravels might be of fluviatile origin.

Mr. Gwyn Jeffyeys thought that if the beds at Cams Wood were marine, some remains of marine organisms might be found in them. If these were absent, he should rather be inclined to regard them as fluviatile.

Mr. J. W. Flower contended that the gravel at Downton could not be of fluviatile origin. He thought, indeed, that the gravel was actually at a higher level than the present source of the river. If this were so, he maintained that the transport of the gravel by fluviatile action was impossible. He further observed that gravels precisely similar, also containing implements, had now been found, as well in the Hampshire area as elsewhere, the transport of which, in his view, could not possibly be attributed to any existing rivers. At Southampton they occur 150 feet above the river Itchen and the sea and considerably inland, at Bournemouth on a sea-cliff 120 feet in height, and at the Foreland (at the eastern extremity of the Isle of Wight) on a cliff 82 feet above the sea and far remote from any river. If, therefore, these deposits were effected by fluviatile agency, it was evident that all traces of the rivers were afterwards effaced by some great geological changes; or, in the alternative, some great geological change, not fluviatile, must have caused the deposit. Upon the whole, he was disposed to conclude, with the French geologists as well as with many eminent Engish authors, that the accumulation of all these superficial drifts was, as the late Sir Roderick Murchison had said, sudden and tumultuous, not of long continuance; and thus it was such as would result from some kind of diluvial action, rather than from the ordinary long-continued action of water.

Mr. Judd pointed out, in contravention of Mr. Jeffreys's views, that in the Fen-district, over large tracts of gravel of undoubtedly marine origin, there are many pits without a trace of marine shells.

Mr. Prestwich, while willing to concede that the implement-bearing gravel beds had been deposited under more tumultuous action than that due to rivers of the present day, was still forced to attribute the excavation of the existing valleys and the formation of terraces along their slopes to river-action. He showed that Mr. Flower's argument as to the present level of the source of the river was of no weight, as the country in which it had its source was formerly, as now, at a much higher level than the gravel at Downton. As to the absence of marine shells at Cams Wood, he cited a raised beach in Cornwall which, in company with Mr. Jeffreys, he had examined for a mile without finding a trace of a shell, though for the next half mile they abounded. There was the same difference between the raised beaches at Brighton and at Chichester. He was obliged to Mr. Codrington for his correction as to the level at Cams Wood, though the pit was at a higher elevation than the one to which Mr. Codrington had alluded.

  1. Quart. Journ. Geol. Soc. 1859, vol. xv. p. 215.
  2. Ibid. 1870, vol. xxvi. p. 528.
  3. Evans, Quart. Journ. Geol. Soc. 1864, vol. xx. p. 188.
  4. Codrington, ibid. vol. xxvi. p. 537.