THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE II. VOL. II. 



No. XII.— DECEMBER, 1875. 



OBIGIUAL ABTICLES. 



I. — The Cause of the Glacial Period, with Reference to the 

 British Isles. 1 



By Charles Bicketts, M.D., F.G-.S. 



IT is a fact universally accepted that, within a period comparatively 

 recent, extensive districts in North America and in Europe, now 

 fruitful and luxuriant, were covered with a thick mantle of snow 

 and ice ; and their valleys were filled with glaciers, which extended 

 into the sea, and, breaking off at their extremities, floated away as 

 icebergs. 



The causes which produced a temperature of such severity, as the 

 evidences upon which this opinion has been founded indicate, have 

 excited much speculation. The theory which of late has found most 

 advocates is that proposed by Mr. Croll : — That the winters during 

 this, the Glacial Period, happened in aphelion, when, as a result 

 of a greatly increased eccentricity of its orbit and the precession 

 of the Equinoxes, the Earth was eight and a half millions of miles 

 further distant from the Sun during winter than it is at present; 

 that therefore the winters would have been longer and the cold 

 more intense; that the North Polar regions were entirely covered 

 with a thick capping of ice, so great that the accumulation caused 

 a displacement of the Earth's centre of gravity ; and to this cause 

 he attributes the submergence of the land which is constantly found 

 where evidences of glaciation have been observed. He also justly 

 concludes that the so invariable occurrence of submergence along 

 with glaciation points to some physical connexion between the two. 

 But the submergence of Greenland, beneath its present rapid accu- 

 mulation of snow, cannot be referred to such a cause as a change 

 in the Earth's centre Of gravity, for at the same time and in about 

 the same latitudes — in Norway and Spitzbergen — the land is rapidly 

 rising. It seems not improbable that the recent recession of the 

 glaciers in Norway may account for the rise of land there, in con- 

 sequence of the removal of pressure, and, to a similar cause, its 

 occurrence, subsequent to the Glacial Period, may be attributed. 



I have elsewhere (Geol. Mag. Vol. IX. page 119) attributed this 

 subsidence during the Glacial Period to the effects of the pressure 

 which this increased mass of snow would have in forcing downwards 



the crust of the earth into its fluid substratum ; basing my opinion, 



upon the constant occurrence during all geological time of evidences 



1 Bead before the British Association (Section C.) at Bristol, August, 1875. 



DECADE II. — VOL. II. NO XII. 37 



