CHAPTEE lY. 



PHYSICAL AND CLIMATAL CONDITIONS 



(Continued). 



II. — Causes of Glaciation and Distribution of Erratics — Continued. 

 2.— SEA-BORNE ICE. 



2. We now come to the question of dispersion of 

 boulders and formation of boulder-clay and striated 

 surfaces by floating ice, whether formed on the sea or 

 derived from the ends of glaciers discharging at the level 

 of the sea. Here we may take for granted the great 

 submergence of the North American continent, first in 

 the early glacial period, and subsequently to a still 

 greater extent in the later glacial period, and that this 

 submergence was in the earlier period differential, affecting 

 the plains and not the mountains. 



I shall first quote here a letter received several years 

 ago from my friend, Dr. John Eae, F.E.S., a traveller of 

 almost unrivalled arctic experience,* and which shows 



* September, 1882, The same facts are referred to in a paper by 

 Dr. Rae in the Journal of the Physical Society, 1881. 



