564 Notices of Memoirs — R. D. Oldham — Rocks of Ullswater. 



genus Lioceras,^ but Buckman^ has made it the type of a new genus, 

 Pohjplectus. The Museum, then, is fortunate in possessing this type- 

 specimen, for it is not only the type of Zieten's species Amm. 

 discoides, but also the type of Buckman's genus Polyplectus. 



I. — The Basal (Carboniferous) Conglomerate of Ullswater 

 AND ITS Mode of Origin. By E. D. Oldham, Geological Survey 

 of India.^ 



ON the western shore of Ullswater, near its lower end, a good 

 section has recently been exposed of the basal conglomerates 

 variously ascribed to Old Red or lowermost Carboniferous age. This 

 conglomerate has been considered as glacial in its origin, but does 

 not appear to the author to present any true glacial characteristics. 

 It contains angular and subangular blocks of all sizes, which are not 

 scattered indiscriminately, but are ari-anged with a distinct, though 

 obscure, banding. In the admixture of blocks of all sizes and the 

 absence of rounded boulders, it differs from the known river deposits 

 of temperate climes, and more closely resembles the accumulations of 

 debris which result from cloud-bursts than any other form of deposit 

 which can be observed in the British Isles at the present day. The 

 conglomerate cannot, however, be reasonably attributed to any such 

 local deposits ; its true analogue must be looked for in the dry 

 regions of Western and Central Asia, where all rainfall rushes off 

 the bare hills, producing an effect very like that of a cloud-burst in 

 our own climate, and causing a mixed mass of water, silt, and stones 

 to rush down the river channels, which are dry or carrying only 

 a feeble stream in ordinary times. This mass of material is carried 

 out from the hills, and forms a deposit with a gently sloping surface 

 extending for miles into the open country. Carried along in this 

 manner the rock-fragments do not undergo the rounding which they 

 suffer in a more permanent torrent, and are deposited, on the sudden 

 subsidence of the flood, in a mixed mass of fragments of all sizes. 

 The sections exposed along the roadside near the foot of Ullswater 

 not only exhibit a rude trending, due to the action of successive 

 floods, but also show patches of current - bedded, fine - grained, 

 gravelly material, representing the action of the feebler stream 

 which continued after the passage of the flood. 



The conclusion drawn is that the conglomerate is a torrential 

 deposit, formed on dry land, near the foot of a range of hills, in 

 a generally dry climate, varied by seasonal or periodical bursts of 

 rain. The red colour of the fine-grained material suggests tropical 

 or sub-tropical conditions, as the formation of red soils is at the 

 present day so much more common in tropical than in temperate 

 regions that it may almost be regarded as a characteristic of a hot 

 climate. 



1 Originally spelt Leioceras. 



2 S. S. Buckman : Inf. Oo. Amm. (Mon. Pal. Soc), pt. iv (1890), p. 214. 



2 Read before the British Association, Section C (Geology), Bradford. Sept., 1900. 



