288 THE POPULAR SCIENCE MONTHLY. 



advantage of allowing the continent to stand still instead of sinking it 

 several thousand feet below the ocean-level. 



Mr. De Kay claimed that the bowlders originated at or near the 

 places in which they now lie , that they are the remains of ancient 

 peaks of primitive rock that have since been demolished by earth- 

 quakes and by atmospheric forces, the sites covered by detritus, and 

 concealed from the observer. This was announced in 1828, but it 

 made no headway, probably from the fact that these bowlders lie on 

 the surface not only where primitive rocks abound, but also overbroad 

 areas where the primitive rocks are buried thousands of feet below 

 later sedimentary formations, such formations being intact over the 

 whole area. 



In 1837 Prof. Louis Agassiz propounded that theory known as the 

 glacier theory in a paper read before the Helvetic Society of Natural 

 History in his native country, Switzerland. It is thus concisely stated 

 by Mr. Charles McLaren : " It was deduced from a careful study of 

 the phenomena attending glaciers. . . . The Swiss philosopher ad- 

 vanced step by step. He satisfied himself that in the Alpine valleys, 

 where glaciers still exist, they once rose to a higher level, and ex- 

 tended farther down into the low country than they now do. Next he 

 discovered indications of their former existence on Mont Jura and over 

 the whole Swiss valley ; and, connecting these with similar indications 

 found in the Vosges, the Scandinavian mountains, and elsewhere, and 

 with the well-known fact of sheets of ice covering the northern shores of 

 Siberia, and entombing the remains of extinct species of animals, he came 

 to the conclusion that, at a period, geologically speaking, very recent, 

 all the Old World north of the 35th or 36th parallel had been enveloped 

 in a crust of ice. Whence the cold came which produced this effect, 

 and why it afterward disappeared, are questions he did not feel him- 

 self bound to answer." This theory had been suggested before by 

 Venetz, but had been applied by him only to the region of the Alps. 

 Prof. Agassiz afterward more fully worked out his theory, giving facts, 

 and careful measurements, and calculations, in his famous work entitled 

 " Etudes sur les Glaciers." 



Prof. Agassiz supposes that the eastern Alps were upheaved when 

 the coating of ice was on the surface, this being the last cataclysm 

 that has visited Europe. By this upheaval of the Alps the ice was 

 disturbed, like the rocky formations. This was accompanied or fol- 

 lowed by a higher temperature, and the thawing of the ice, which pro- 

 duced torrents and consequent valleys of erosion. The floods which 

 followed the upheaval of the Alps were sufficient to float icebergs con- 

 taining blocks of rock that might be deposited in different places, the 

 water being at least 300 feet deep, and the agent that carried and de- 

 posited the fine drift in the valleys below. The catastrophe which en- 

 veloped the northern regions in ice was sudden, according to Prof. 

 Agassiz, but the retreat of the glacier was slow. 



