IXTERGLACIAL EPOCHS. 



3i5 



cut that impediment across and so drain itself. The process of 

 excavation would, however, be more tedious than might at first 

 be supposed. The remains of the bar are still found clinging to 

 the slopes of the mountains in the form of a mass of indurated 

 conglomerate and coase debris. It is highly probable that long 

 before the glacier had disappeared much of its moraine may 

 have become thus hardened by the infiltration of superficial 

 water. Many of the rock-fragments consist of limestone, while 

 the hills around are composed largely of calcareous strata. We 

 are not to suppose, therefore, that the bar of morainic detritus 

 would be as readily removed as one composed of the debris of 

 crystalline rocks in a country where the superficial water contains 

 only a very small percentage of calcareous matter. And the same 

 remarks apply to the bar across the mouth of the Yal Gandino, 

 which is a mass of more or less indurated conglomerate. A 

 shallow lake, therefore, would continue to exist for some time 

 during the genial epoch that supervened after the dissolution 

 of the glacier in the Yal Camonica. It was then that a rich 

 flora crept up the Alpine valleys from the plains of Italy, and 

 the great Pleistocene mammals found a congenial home in 

 such secluded vales as that of Clusone and the Yal Borlezza. 

 The lake, no longer turbid with glacial mud, now favoured 

 the accumulation of pure white marl, and fish abounded in 

 its waters. But eventually these genial conditions came to 

 a close ; the mammalia retreated, the rich vegetation disap- 

 peared. Once more the Yal Camonica filled with ice, and the 

 glacier dilating into the Yal Borlezza threw its lateral moraine 

 upon the surface of the interglacial deposits. The advent of 

 milder conditions and the final dissolution of the glacier then 

 permitted the river Borlezza to cut its way down into the deep 

 narrow trench through which its waters now rush to join the 

 Lago d'Iseo. 



The Yal Adrara and the Yal Forestro each contain relics of 

 ancient glacial lakes which from Stopanni's description would 

 appear to have experienced the same cycle of changes as the 

 larger valleys which I have just described. 



