THEORY OF MR. LYELL. — ASTRONOMICAL CAUSES. 359 



portion of land and water, which may serve in a considerable degree 

 to explain, why one situation should enjoy more heat than the other. 



Mr. Lyell has advanced a theory respecting the former high tem- 

 perature of northern latitudes, in which, by many local illustrations 

 and ingenious arguments, he attempts to prove, that a great change 

 in the relative position of the land and sea, would be sufficient to ac- 

 count for the excess of the former temperature, over that now en- 

 joyed in northern regions. He states two extreme cases, which, 

 could they ever occur, must produce an important change in the cli- 

 mate of Europe. Were the land between the tropics to be sub- 

 merged under the ocean, and an equal portion of mountainous land 

 to be raised in the polar circles, the cold of those regions would be 

 much increased, and the heat between the tropics would be very 

 greatly diminished ; by the joint operation of these causes, the cli- 

 mate of the southern parts of Europe might become as cold as that 

 of Siberia. On the contrary, were all the land in high latitudes to 

 be submerged, and an equal quantity of land to be raised above the 

 sea, near the equator, the mean temperature of a great part of Eu- 

 rope might be sufficiently increased, to support the vegetation of 

 tropical climates. The theory of Mr. Lyell is entirely original, and? 

 throws much light on the causes which affect the climate of various 

 countries in the same parallels of latitude ; and could we grant that 

 the change of land and sea had ever been so complete as what he 

 has imagined, the conclusions deduced therefrom would be undeni- 

 able : but so many conditions are required to effect such extreme 

 changes, that we must regard their occurrence as merely possible, 

 and La Place, in his Essai Philosophique sur les Probabilites,^^ has 

 shown, that between events which are merely possible, and those- 

 which the philosopher should regard as probable, there is an almost 

 immeasurable interval. Nor can the theory of Mr. Lyell be well 

 reconciled with the occurrence of the remains of such immense 

 multitudes of tropical animals and plants, in countries bordering the 

 arctic circle, because, to increase the temperature of Europe in a 

 considerable degree, the theory would require all the land in higb 

 northern latitudes to be submerged ; but this is precisely the very 

 land on which the elephants flourished. 



The cause which has effected a change in the temperature of the 

 earth, must probably be sought for, either in the earth itself, or in 

 some change in its orbit, or in the relative position of its axis. Did 

 the severe laws which analysis and observation have established in; 

 astronomy, allow the geologist to admit a slow revolution of the globe, 

 round two opposite points of the present equator, each part of the 

 earth would in succession be brought between the tropics ; and if 

 we could suppose the axis of diurnal rotation, to preserve the same 

 inclination to the ecliptic as at present, we should have all the con- 

 ditions required, for explaining the former high temperature of polar 

 regions. The spheroidal form of the globe appears, however, to 



