THE FORMER EXTENSION OF GLACIERS. 1 63 
cavities.* This deposit originally formed a more or 
less continuous sheet, from 30 to 50 metres in thick- 
ness, deposited by the water flowing from the melt- 
ing glaciers, but has been to a great extent removed, 
fragments only remaining here and there on the high 
ground. It is remarkable that it contains no traces 
of Julier or Puntaiglas Granite,** probably because 
these rocks were still covered by the Crystalline 
schists. The lateral Moraines of this period are un- 
known, but the ground Moraines are sometimes well 
developed. Under the Deckenschotter on the Uetli- 
berg they attain a thickness of 2 to 20 metres. 
They were probably for the most part destroyed by 
the glaciers during the Second Ice Age. 
The Second Ice Age is represented by gravel-beds, 
still far above the present valleys, though at a lower 
level, and by outer and upper moraines, for an in- 
stance in the Zurich district those of Hongg, of the 
Albis, etc. The terminal moraines of this period 
were however probably beyond the boundaries of 
Switzerland. 
Th? Third Ice Age is indicated by the lower 
terraces and the moraines in the valleys. In that 
of Zurich, the Moraine of Killwangen was pro- 
* This structure does not occur in the true Nagelfiue. 
** Du Pasquier, Beitr. z. Geol . K. d. Schw L. XXXI. 
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