Ice in Streams 81 



life gathered upon the stone ledges, above which these 

 miniature floes are harmlessly drifting. There are 

 great black patches of Simulium larvae, contrasting 

 strongly with the whiteness of the snow. There are 

 beautiful green drapings of Cladophora and rich red- 

 purple fringes of Chantransia, and everywhere amber- 

 brown carpetings of diatoms, overspreading all the 

 bottom. But if one stand in the same spot in the 

 spring, after the heavy ice of winter has gone out, he 

 will see that the rocks have been swept clean and bare, 

 every living thing that the ice could reach having gone. 



The grinding power of heavy ice, and its pushing 

 power when driven by waves or currents, are too well 

 known to need any comment. The effects may be seen 

 on any beach in spring, or by any large stream. But 

 there is in brooks and turbulent streams a cutting with 

 fine ice rubble that works through longer periods, and 

 adds the finishing touches of destructiveness. It is 

 driven by the water currents like sand in a blast, and it 

 cleans out the little crevices that the heavy ice could 

 not enter. This ice rubble is formed at the front of 

 water falls under such conditions as are shown in the 

 accompanying figure of Triphammer Falls at Ithaca. 

 The pool below the fall froze first. The winter increas- 

 ing cold, the spray began to freeze where it fell. It 

 formed icicles, large and small, wherever it could find a 

 support above. It built up grotesque columns on the 

 edge of the ice of the pool beneath. It grew inward 

 from the sides and began to overarch the stream face; 

 and then, with favoring intense cold of some days dura- 

 tion, it extended these lines of frozen spray across the 

 front of the fall in all directions, covering it as with a 

 beautiful veil of ice. 



The conditions shown in the picture are perfect for 

 the rapid formation of ice rubble. From thousands of 

 points on the underside of this tesselated structure 



