260 PEOCEEDINGS OF THE GEOLOGICAL SOCIETT. [April 14, 



middle glacial period. At Somerleyton Brick-kiln, near Lowestoft, 

 a perfectly similar bed occurs between the drift and sand (Nos. 

 3 and 4). 



DlSCUSSIOK-. 



The President inquired whether the perpendicular wall of chalk 

 shown in the section could be due to the action of a glacier, as sup- 

 posed 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. Eyans thought it possible there might have been a valley 

 originating in a large fissure, and partly filled up with reconstructed 

 glacial deposits. 



Prof. Eamsay 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 Poderntjovo, near Yolterra. 

 By E. J. Beor, Esq., E.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| 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 Yal di Bruno, Val di Pecora, Yal di Cornia, and Yal di 

 Cecina), in being purely of marsh origin, while they are estuarine. 



