SUTHERLAND, DAVTS' STRAIT AND BAFFIN'S BAY. 363 



gravel or mud, moraines are raised to a height of several feet. 

 The wind ceasing and high tides proving favourable, the ice again 

 withdraws from the coast, carrying with it large accumulations of 

 the loose shingle of the beach, which it deposits in the surrounding 

 seas, after travelling several hundred miles. The moraines it had 

 raised are not wholly obliterated, and as winter proceeds to hem 

 the coast with a fringe of ice, they cause an irregularity in Ihe 

 surface of the latter by the rise and fall of the tides, which results 

 in a large portion of their contents, mud, sand, shingle, and perhaps 

 also traces of animal and vegetable matter, being included in the 

 new ice formation. This process ceases altogether only with the 

 return of summer, and then the coast-ice, varying in thickness from 

 two or three up to twenty or more feet, according to the degree of 

 cold, the stillness of the water, and the extent of the rise and fall 

 of the tides, is subject, in some localities at least, to the power 

 exerted by debacles in loading it with foreign matter. Thus 

 freighted, it withdraws from the shore when the straits and inlets 

 open out, and drifts many hundred miles before it is dissolved by 

 the action of the sun and the water, and yields itself and its care- 

 fully bound cargo to the sea. We find this occurring every season 

 on the south shore of the North-Georgian Islands ; but from the 

 testimony of numerous travellers,* it occurs on a magnificent 

 scale at the entrances of the great American and Siberian rivers 

 which discharge their waters into the Arctic Seas. 



Polar Currents, — The necessity there is for currents into the 

 Polar Seas to keep up their mean salinity will become obvious when 

 we reconsider the vast amount of fresh water which enters them 

 in the form of icebergs from the glaciers. That there are currents 

 out of the Polar regions is sufficiently clear ; were there no such 

 currents, evaporation alone from the surface of the sea, the greatest 

 part of which is generally covered with ice, would fail to remove 

 the excess carried by the annual crop of icebergs ; and then we 

 should have an icy pile ever growing and gradually extending 

 into the Temperate zone. The difference of temperature observed 

 by the navigator in the waters of the eastern and western shores 

 of the North Atlantic, amounting, as it does, to nearly 30° of 

 Fahrenheit's thermometer in lat. 59° during the warmest months 

 of the year, affords the best possible proof of the existence of 

 currents in the two directions we have indicated. In Davis' 

 Strait, although on a much smaller scale, there is also a difference 

 in the temperature of the sea on its two shores. On several 

 occasions during the late expeditions in search of Sir John Franklin, 

 while the ships were crossing that strait from east to west a fall 

 of a few degrees was observed. This accounts pretty accurately 

 for the fact that the east shore during a great part of the year 

 keeps clear of ice, while the opposite is for the most part encum- 

 bered ; and the greater mildness of the climate on the east side 

 arises from the same cause. Allusion need not be made here to 

 the late President's Paper on the temperature of the North of 



Principles of Geology, Seventh Edition, page 86. 



