Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/373

 was supposed to be a continuation of the Hessle bed, whereas the excavations and subsequent borings showed that the Hessle Sand thinned out at the west end of the dock. To the westward of the west end of the dock the peat, Hessle Clay, and Hessle Sand have been removed by the scour of the Hunber down to the surface of the Purple Clay, and the more modern deposits of Humber sand and silt repose directly on the latter. In the section in vol. xxiv. of the Society's ' Proceedings,' above referred to, the lower part of this silt deposit, described as sand in the borings, is, in the writer's opinion, wrongly shown as a continuation of the Hessle- Sand bed. Several borings were made in the foundation for the dock -wall towards the west end of the dock ; the thin bed of Hessle Sand reached by these borings was similar in colour to that found at the east end of the dock, where the Hessle Sand also thins out. As the bed diminished in thickness it became similar in colour to the adjoining clays. Good sections, about 500 feet in length, of the junction of the two clays with the Hessle Sand, the latter reduced to a thickness varying from 2-1/2 feet to 5 inches, were exposed in the excavations for the foundations of the lock at the east end of the dock, which were carried down to the surface of the Purple Clay. Throughout those sections the sand was nowhere absent, and the junction with the two clays was very distinct. Where the bed was thick the sand was of a bright yellow colour, much cross-bedded, and composed of fine rounded grains of quartz, mixed with a considerable proportion of grains of chalk. This Hessle sand was probably reconstructed out of the Purple Clay in the same manner that the Hessle sand and gravel at Kelsey Hill have, in Mr. Prestwich's opinion, been reconstructed out of the boulder clays. Two sections, each about 1000 feet in length, show accurately the junction of the Hessle Sand and the Purple Clay. There was no intermingling of the sand and clay. The Hessle Sand was removed from the surface of the Purple Clay for the foundation of the dock-walls, for a width of 30 feet along the lines of these sections. The appearance of the surface of the Purple Clay shows it to have been consolidated before the deposition of the sand. A depression about 6 feet in depth, and apparently due to erosion, crossed the section at right angles. On one side the clay formed a steep face ; and the bottom of the hollow was strewed with small gravel and scratched and rolled stones. Sometimes boulders were found on the surface of this clay too large to be removed by the current which probably swept the surface of the clay before the deposition of the Hessle Sand.

The borings taken at the east end of the lock showed the purple clay to be very compact, and free from stones and pot-holes ; these borings were taken to ascertain the source of some springs which burst out in the foundations before the excavations were completed. With one exception, they extended to a depth of 58 feet below high water, nothing but the solid clay being met with below the surface of the Purple Clay. The water from the springs was brackish, and was in all cases charged with from 2 to 5 per cent, of reddish-yel-

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