INDUSTRIAL PROGRESS DURING THE YEAR 1874. lxxv 



jecting all the other explanations of the supposed change of 

 temperature implied in these glacial periods, he adopts the 

 view that our sun is a variable star. The sudden increment 

 of its heat by one half would make the tropical region the seat 

 of enormous evaporation, and the polar regions one of excess- 

 ive precipitation, resulting in the great circumpolar glaciers. 



Croll, who has done so much to develop the hypothesis of 

 universal land-glaciation, has discussed the question of the 

 glacial phenomena of Southern England, and maintains that 

 a great ice-sheet once filled the Baltic and the German Oceans, 

 and spread over to England, while Prestwich and Whitta- 

 ker maintain the submarine origin of the glacial drift of 

 Southeastern England. 



Evans, the president of the Geological Society of London, 

 rejects the doctrine of great ice-caps, since it involves the de- 

 struction and recreation of the entire fauna and flora of re- 

 gions. According to McKenna Hughes, the hypothesis of 

 ice-caps accounts for no facts which can not be otherwise 

 explained, while it involves great physical difficulties, and is 

 quite inconsistent with the continuity of the forms of life 

 from pre-glacial to post-glacial times. He questions wheth- 

 er glacial phenomena were ever simultaneous even over one 

 hemisphere, and maintains that in Scandinavia there is evi- 

 dence that boulders have been carried northward as well as 

 southward. Campbell, from his studies in Northern Russia, 

 while admitting the former existence of local ice-systems, re- 

 jects the notion of a universal ice-cap, and attributes much to 

 equatorial and polar currents, such as now move in the Atlantic. 



Dawson, in like manner, has shown that drift on Prince 

 Edward's Island includes not only boulders from the north- 

 ward, coming from Labrador, but others from the southward, 

 from the hills of New Brunswick. He has again discussed the 

 phenomena of glacial drift in the St. Lawrence Valley, and 

 points out the fact that on the south side of the mountain 

 of Montreal the earthy paleozoic limestones have been deep- 

 ly affected by sub-aerial decay ; while on the northeast side 

 there is no trace of this, but the same limestones are, on the 

 contrary, polished and glaciated by a force which, by its ac- 

 tion on the transverse trap dikes, is shown to have been 

 from the northeast, or up the valley of the St. Lawrence. He 

 concludes, that it is impossible that these results could have 



