INTERGLACIAL EPOCHS. 313 



been considerably farther north than the present. Its inter- 

 glacial and postglacial course would be determined by the 

 contour of the cone, de dejection across which the lake would 

 overflow at the lowest part, which, of course, need not have 

 coincided with the preglacial course of the Bonma. 1 



But while I agree with Stopanni that the lake was formed 

 in the way he supposes, I cannot go with him when he main- 

 tains that all the lacustrine deposits were laid down during the 

 piling up of the embankment, that is to say, in other words, 

 during a glacial epoch. The character of the flora and fauna of 

 Leffe and Borlezza will not permit of this supposition. It is 

 impossible to believe that at a time when all the great valleys 

 of the Alps were filled to overflowing with enormous glaciers, 

 many of which deployed upon the plains of Biedmont, Lombardy, 

 and Venetia, and when all the low grounds of Switzerland were 

 buried under an enormous mer de glace, which flowed north to 

 within a few miles of the Danube, and descended in the west to the 

 low-lying tracts of Dauphiny, it is impossible, I think, to believe 

 that at such a time the climate of two mountain- valleys like the 

 Val Gandino and the Yal Borlezza could have supported a rich 

 flora, comprising magnolia, box, walnut, etc., or had for their 

 occupants elephants, rhinoceroses, oxen, and deer. Nor do the 

 stratigraphical appearances justify us in holding such a view. 

 The lignites, with their associated shelly clays and marls, are 

 of interglacial age — they separate in fact two glacial epochs. 

 During the first of these epochs we may believe the Serio to 

 have blocked up the Yal Gandino with its cone de dejection. 

 The glaciers then melted away, and perennial ice was confined 



1 Another view suggests itself as a possible explanation of the phenomena. 

 The lacustrine deposits may occupy an old rock-basin. The appearances in the 

 valley below the lignite-workings do indeed seem to indicate as much. But if so, 

 how was that rock-basin formed ? The geological structure of the valley hardly 

 admits of us supposing that the limestones may have been undermined by acidu- 

 lated waters, and so have given rise to a rock-hollow by subsidence. Nor have we 

 any evidence of glacial action to lead us to infer that the hollow might have 

 been excavated by a local glacier. The mountains surrounding the Val Gandino 

 show no trace of glaciation ; no erratics occur, neither did I encounter any in 

 the Yal Seriana below the confluence of the Eomna with the Serio. 



