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[Boor TIT. 

96 DYN AMIORE GEOLOGY: 
above water.’ Icebergs of the largest size consequently require 
water of some depth to float them, but are sometimes seen 
aground. In the Antarctic regions, where one vast sheet of ice 
envelopes the land and protrudes into the sea as a long, lofty ram- 
part of ice, the detached icebergs often reach a great size, and are 
characterized by the frequency of a flat tabular form (Fig. 160). 



































































































— 
aims 
Fic. 160.—TapnuLar IcEBERG DETACHED FROM THE GREAT ANTARCTIC 
IcE-BARRIER. (WILKES.) 
II. Geological Work. (1.) Influence on Climate.—Were 
there no agencies in nature for distributing temperature, there would 
be a regular and uniform diminution in the mean annual temperature 
from equator to poles, and the ¢sothermal lines, or lines of equal heat, 
would coincide with lines of latitude. But no such general corre- 
spondence actually exists. A chart of the globe with the isothermal 
lines drawn across it, shows that their divergences from the parallels 
are striking, and most so where they approach and cross the ocean. 
Currents from warm regions raise the temperature of the tracts into 
which they flow; those from cold regions lower it. The ocean, 
in short, is the great distributor of temperature over the globe. As 
an illustration the two opposite sides of the North Atlantic may be 
taken. The cold Arctic current flowing southward along the north- 
east coast of America reduces the mean annual temperature of that 
region. On the other hand, the Gulf Stream brings to the shores 
of the north-west of Europe a temperature much above what they 
would otherwise enjoy. Dublin and the south-eastern headlands of 
Labrador lie on the same parallel of latitude, yet differ as much as 
18° in their mean annual temperature, that of Dublin being 50°, and 
that of Labrador 32° Fahr. Dr. Croll has calculated that the Gulf 
Stream conveys nearly half as much heat from the tropics as is 
received from the sun by the entire Arctic regions.” 
(2.) Hrosion, A. Chemical.—The chemical action of the sea upon 
the rocks of its bed and shores has not yet been properly studied.* 
* On flotation of Icebergs, see Geol. Mag. (2nd sec.), iii. pp. 308, 879 ; iv. 65, pp. 135. 
* See a series of papers by him on the “Gulf Stream and Ocean Currents” in 
Geol. Mag. and Phil. Mag. tor 1869,'1870-74, and his work “ Climate and Time.” 
* See Bischol’s “ Chemical Geology,’’ vol. i. chap, vii. 

