PRELIMINARY CONSIDERATIONS. 69 



snow comes from the clouds, and these again 

 originate from the vapours which the sun causes 

 to be absorbed from the ocean. Without the sun's 

 heat, we should have no water vapour in the 

 atmosphere ; without vapour, no clouds ; without 

 clouds, no snow ; without snow, no glaciers. The 

 ice of glaciers, therefore, owes its origin indirectly 

 to the sun's heat. It has been supposed that if the 

 sun's heat diminished, larger glaciers would form 

 than those existing to-day, but the diminution of the 

 solar heat would infallibly reduce the amount of 

 water vapour in the air, and would thus stop the 

 very source of glaciers. 



Mr. Falsan even admits that without a change of 

 the mean annual temperature (p. 201) of Europe, 

 the central portions of our continent might at this 

 period have enjoyed an insular climate. This more 

 equable and humid climate could, within certain 

 limits, favour the development of the ancient glaciers 

 by increasing the snowfall and slackening the summer 

 rate of melting. 



It seems evident then, according to these views, 

 that with a comparatively slight change of the 

 atmospheric conditions in the British Islands, we 

 might have glaciers back again on all our highest 

 mountain ranges in England, Scotland, and Ireland. 

 But a widespread belief seems to prevail that the 

 presence of glaciers implies a very low temperature. 

 Snow and ice, however, are formed as soon as the 

 temperature falls below freezing point; it does not 



