3G3 



CHAPTER XVI. 



TRANSPORTATION OF SOLID MATTER BY ICE. 



CARRYING POWER OF RIVER-ICE — ROCKS ANNUALLY CONVEYED INTO THE 

 ST. LAWRENCE BY ITS TRIBUTARIES — GROUND-ICE; ITS ORIGIN AND TRANS- 



PORTING POWER GLACIERS — THEORY OF THEIR DOWNWARD MOVEMENT 



SMOOTHED AND GROOVED ROCKS THE MORAINE UNSTRATIFIED — TERRACE OR 



BEACH FORMED BY A GLACIER-LAKE IN SWITZERLAND — ICEBERGS COVERED WITH 



MUD AND STONES LIMITS OF GLACIERS AND ICEBERGS THEIR EFFECTS ON 



THE BOTTOM WHEN THEY RUN AGROUND PACKING OF COAST-ICE BOULDERS 



DRIFTED BY ICE ON COAST OF LABRADOR — BLOCKS MOVED BY ICE IN THE 

 BALTIC. 



The power of running water to carry sand, gravel, and frag- 

 ments of rock to considerable distances is greatly augmented 

 in tliose regions where, during some part of the year, the 

 frost is of sufficient intensity to convert the water, either at 



the surface or bottom of rivers, into ice. 



This subject may be considered under three different 



heads : — first, the effect of surface-ice and ground-ice in en- 

 abling streams to remove gravel and stones to a distance ; 

 secondly, the action of glaciers in the transport of boulders, 

 and in the polishing and scratching of rocks ; thirdly, the 

 floating off of glaciers charged with solid matter into the sea, 



and the drifting of icebergs and coast-ice. 



River-ice. — Pebbles and small pieces of rock may be seen 

 entangled in ice, and floating annually down the Tay in 

 Scotland, as far as the mouth of that river. Similar obser- 

 vations might doubtless be made respecting almost all the 

 larger rivers of England and Scotland; but there seems 

 reason to suspect that the principal transfer from place to 

 place of pebbles and stones adhering to ice goes on unseen 

 by us under water. For although the specific gravity of the 

 compound mass may cause it to sink, it may still be very 



