Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/180

 1. On Lower Tertiary Deposits recently exposed at Portsmouth By C. J. A. Meyer, Esq., F.G.S.

The excavations in progress at Portsmouth in furtherance of the works known as the " Dockyard Extension Works," have exposed to view, during the last three or four years, many fine and highly interesting sections in the Lower Tertiaries.

I propose to lay before the Society, by way of record, a brief account of these sections, and of the numerous fossils which have been obtained from them.

The site of the " Extension Works " lies to the east and northeast of the existing Dockyard. A description of the works themselves would be out of place in this paper ; I shall therefore confine my mention of them to such points only as may serve to illustrate the geology of the district.

Previously to the commencement of these works, in 1867, the ground intended to be occupied was, for the most part, a vast mud-flat, covered at every tide by the waters of the harbour. The mud, of which I shall have more to say hereafter, was of the soft and sticky character so prevalent in tidal basins, and attained over some parts of the area to the formidable depth of from 35 to 40 feet.

In 1868 the sea was excluded by means of a dam of sheet-piling ; and the enclosed area has been since reduced, by pumping and deep drainage, to almost perfect dryness to the depth of 40 feet beneath low water.

Excavations had been already commenced in the higher portion of the ground before the shutting out of the sea- water; and in 1867 I heard from my brother, Mr. C. H. Meyer, that fossils of the London clay were being met with in abundance.

In the spring of 1868, when I first visited the works, a fine section nearly 500 feet in length was exposed to a depth of 60 feet. It consisted of : —

Gravel 10 to 20 feet.

Stiff clay, with Septaria 30 to 40 feet.

A band of rounded black pebbles in clay 8 inches

Sands and shell-rock 10 feet.

The fossils of the clay with Septaria were clearly London-clay species. Those of the sands and shell-rock appeared to represent more nearly an equivalent to the Bognor fauna ; but I was puzzled by many of the species, and determined to watch the progress of the excavations.

New sections have been from time to time exposed since 1868, until in August of the present year (1870) the excavations had so far progressed as to have opened out clear and nearly continuous sections of all the strata likely to be seen within the area of the works.

Description of Strata.

The strata exposed in 1870, exclusive of alluvial deposits, amounted to a thickness of 97 feet. To this must be added a thickness of