402 G. W. Bulman — Glacial Geology. 



channel holds good, not only in the case of large and deep rivers, 

 but also in the case of so comparatively insignificant a stream as 

 this, which at certain seasons of the year runs almost dry and has 

 so trifling a volume of water that it disappears completely in the 

 Kura Steppe without reaching either river or lake of any kind. 

 And yet this small volume of water has been able to execute so 

 grand a piece of erosive work. 



IV. — On the Sands and Gravels Intercalated in the 



BOTJLDER-OLAT. 



By G. W. Bulman, M.A., B.Sc, Corbridge-on-Tyne. 

 {Concluded from the August Humber, p. 348.) 



On the Italian side of the Alps a similar set of lignite beds occurs 

 as on the Swiss side. But these Italian lignites, although occurring 

 heneath, are not underlaid by glacial deposits. 



Evidently, then, they afford even less evidence of an interglacial 

 period than those on the Swiss side ; and this Prof. Geikie himself 

 seems to confess ; for he writes of them : 



" They are clearly of older date than any recognizable morainio 

 or diluvial deposits in Northern Italy ; and if it were simply a 

 question of local geology, one could have no good reason for 

 doubting their pre-glacial age." ^ 



And yet, taking them along with the Swiss beds, he finds in them 

 similar witness to an interglacial period. 



With regard to the " marine sands " with which the lignites seem 

 to be contemporaneous. Prof. Geikie considers the evidence of their 

 fossil shells insufficient to establish their pre-glacial age. 



The number of extinct species in the sands is said to be from 

 15 to 20 per cent. ; and if we compare this with the 18 per cent, 

 extinct species of the Norwich Crag, the inference seems obvious 

 that the beds are pre-glacial. 



Prof. Geikie points out, however, that such comparisons are only 

 conclusive when confined to the same geographical area ; and when 

 we substitute the Italian Pliocene for the English, a very different 

 conclusion is suggested. For in the lowest beds of the former the 

 per-centage of extinct shells is 83, and in the Upper 68. If, then, 

 these Italian Pliocene are rightly classed, the lignites must be at any 

 rate Post-Pliocene. But even then, it is still possible they may 

 have been formed before the ice reached the district where they 

 occur, A local geologist, however, the Italian Prof. Gastaldi, does 

 not consider the Italian lignites to be interglacial. At the same 

 time he believes them to be of the same age as the Swiss beds. But 

 if the Swiss lignites lie upon glacial beds, and the Italian below 

 glacial beds, and if they are of the same age, it follows that the 

 lignites must be interglacial. 



The argument seems to hinge on the question whether the organic 

 remains indicate a similar age for the lignites on the two sides of 



^ Great Ice Age, p. 527. 



