3 06 PREHISTORIC E UR OPE. 



these conditions obtained, the valley-slopes in the neighbourhood, 

 according to Stopanni, were clothed with magnolias, sycamores, 

 box-trees, yews, and so forth, — the rhinoceros wandered along 

 the margin of the lake, and fish abounded in its waters. This, 

 however, was before the glacier had reached its greatest develop- 

 ment. " The glacier," he says, " continuing to increase, dilated 

 into the Val Borlezza. The lake, now partially silted up with 

 its own sediment, had become diminished in extent, and the 

 morainic ddbris fell from the side of the glacier upon the surface 

 of the lacustrine deposits," and then the ice finally melted 

 away and permitted the river Borlezza to drain the lake, and 

 eventually to cut a deep trench down through the ancient 

 lacustrine deposits. Thus, in Stopanni's opinion, all the 

 lacustrine beds of the Val Borlezza belong to a period when 

 the gorge of Castro continued to be dammed with ice, and we are 

 to believe that a rich flora, indicative of a climate not less, nay, 

 according to Sordelli, even more, genial than that now enjoyed 

 by the same valley, clothed the hill-slopes, while the great 

 glacier of the Val Seriana filled the broad hollow that extends 

 from Clusone to the river Borlezza. Again, we are to suppose 

 that this ancient lake — dammed with ice, fed by muddy water 

 flowing directly from a glacier, and by numerous lateral streams 

 descending from snow-covered mountains — was nevertheless 

 tenanted by many fish and microscopic organisms, whose calca- 

 reous skeletons gave rise to an accumulation of pure white marl. 

 With these conclusions I cannot quite agree ; but before 

 giving my reasons for this dissent I will describe first the 

 phenomena presented by the famous lignites of Leffe, in the 

 basin of the Val Gandino, which drains into the Val Seriana. 

 The upper section of the Val Seriana has formerly been occu- 

 pied by a large glacier, which descended as far as Clusone, 

 where it abutted upon the flanks of the Pizzo Formico, a mas- 

 sive mountain, which separates the Val Seriana from the Val 

 Borlezza. Here the ice-flow divided, a portion spreading into the 

 Val Seriana, but the main mass creeping eastward, so as to 

 occupy the wide open space that extends from Clusone to the 



