Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/356

 middle glacial period. At Somerleyton Brick-kiln, near Lowestoft, a perfectly similar bed occurs between the drift and sand (Nos. 3 and 4).

Discussion.

The President inquired whether the perpendicular wall of chalk shown in the section could be due to the action of a glacier, as supposed by the author.

Mr. Prestwich suggested that the depressions formed in the chalk in other districts by chemical action might possibly throw some light on the case.

Mr. Evans thought it possible there might have been a valley originating in a large fissure, and partly filled up with reconstructed glacial deposits.

Prof. Ramsay was inclined to accept the solution offered by Mr. Prestwich, and could not see any traces of the action of a glacier.

Mr. Etheridge thought the phenomena might be accounted for by a fault.

Mr. Hughes pointed out that the clay-bed was totally different from any of the beds supposed to have been let down.

Mr. Searles Wood, Jun., in reply, relied on the difference in character of this bed to prove that the case was not the result either of a fault or of beds being let down into a pothole. He had made a mistake in using the word " glacier " instead of " iceberg."

6. On the Lignite Mines of Podernuovo, near Volterra. By E. J. Beor, Esq., F.G.S.

[Abstract.]

The author stated that the deposit of Lignite at Podernuovo, near Volterra, is of lacustrine origin, and consists of two parallel strata of compact coal about 2-1/2 metres ( = 8 feet 4 in.) in thickness, separated by a thin stratum of marl, with marsh-shells. The lower coal-bed lies on a bed of marl with marsh-shells, and the upper bed is covered by a marine formation belonging to the Upper Miocene. The lignite comes to the surface near the Alberese, where it is thrown up in a large mass and extends for a considerable distance. In the Monterufoli valley, where the lignite is worked, its inclination is found to be about 42° at a depth of 40 metres, where it is intersected by an adit-level driven from the surface of the hill for the removal of the lignite. Two galleries have been driven at right angles to this to a distance of 120 metres right and left through the lignite. Some shifts occur bringing the upper bed down nearly to the level of the lower one ; the inclination of the beds diminishes gradually ; and the intervening stratum of marl decreases in thickness, and probably at last thins out altogether. The coal in the upper bed is better than that in the lower one. The author remarked that this lignite deposit differs from those of the neighbouring valleys (such as the Val di Bruno, Val di Pecora, Val di Cornia, and Val di Cecina), in being purely of marsh origin, while they are estuarine.