84 M. Ch. Martins on the 



ture of cold or temperate zones from 10 to 20 degrees in or- 

 der io explain the presence, in the bowels of the earth, of 

 tropical ferns or the animals of warm countries, would with 

 very bad grace, in my opinion, shew alarm at this alteration 

 of the mean annual temperature, although the proposed 

 change takes place in an opposite sense, and the thermome- 

 ter descends instead of ascends. If we admit that the climate 

 of one portion of the globe may have undergone change, it is 

 as legitimate to suppose that it has become colder, as to main- 

 tain that it has become warmer ; and to diminish by 4 de- 

 grees the mean temperature of a country, in order to explain 

 one of the greatest revolutions of the globe, is assuredly one 

 of the least hazardous hypotheses which a geologist may be 

 permitted to form. 



To discuss the causes which have produced this sinking of 

 temperature, — to indicate the geological or meteorological 

 changes which have brought on this long period of cold, ap- 

 pears to me an attempt altogether premature. It would be 

 necessary, before every thing else, to draw up a map of the 

 extension of glaciers ; now, this can scarcely be said to have 

 been attempted even for the Alps, the Vosges, and the moun- 

 tains of Scotland. Ancient moraines exist in the Pyrenees, 

 Altai, Caucasus, and Atlas ; but no one has yet examined the 

 topography of the glaciers which have carried these before 

 them. Sweden, Norway, Denmark, Finland, and North Ame- 

 rica, were covered with great fields of ice. What of a posi- 

 tive nature can, therefore, be said respecting a phenomenon 

 with whose extent we are yet unacquainted % Let us not 

 imitate our predecessors, whose brilliant imagination rested 

 the boldest generalisations on the frail basis of a few insu- 

 lated and incomplete facts. All these hasty works are des- 

 tined to perish. Science has revealed to us a new epoch in 

 the history of our planet ; a vast field opens before natural 

 philosophers, astronomers, and naturalists. Let us not fear 

 to turn a searching look into the depths of this remote dis- 

 tance, the traces of which have been preserved by the sur- 

 face of the earth, but let us reject hypotheses which outstrip 

 facts, and which a fact the most trifling in appearance over- 

 turns without mercy. By the side of the diluvian period, we 



