306 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 1, 



number of these undergo dissolution there the deposition of rocky 

 matter is most active, consisting of angular and rounded fragments, 

 together with sand and mud, a great part of which materials are pro- 

 bably from sources of very opposite character*. 



Coast-ice. — Ice forming on the surface of sea-water is also well 

 known as an agent of importance in conveying away to considerable 

 distances the materials of the sea-coast. "With strong gales the ice 

 in the Arctic Seas is driven in upon the coasts vnt\\ great force, and, 

 if the bottom about the loT^'^-water mark is composed of loose gravel 

 or mud, moraines ave raised to a height of several feet. The wind 

 ceasing and high tides proving favourable, the ice again withdraws 

 from the coast, carrying vrith 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 the 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 carefully bound cargo to the sea. We find this occur- 

 ring every season on the south shore of the North Georgian Islands ; 

 but from the testimony of numerous travellers f, it occurs on a mag- 

 nificent 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 re- 

 consider 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, 

 amovmting as it does to nearly 30° of Fahrenheit's thermometer in 

 lat. 59° during the warmest months of the year, affords the best pos- 

 sible proof of the existence of currents in the two directions we have 

 indicated. In Davis' Straits, although on a much smaller scale, there 



* See also Col. Sabine's Observations, Brit. Assoc. Sections, 1843. 

 t Principles of Geology, Seventh Edition, page 86. 



