RevieiDS — Prof. N. 8. Shaler — On Glaciers. 85 



crevasses, seracs, all which are exemplified in the heliotypes. Wood- 

 cut diagrams are also added in the letterpress. From Switzerland 

 the author passes to Greenland, describing what is known of glaciers 

 there, and their icebergs. They seem to differ in many things, among 

 others the comparative absence of moraines. 



The consideration of ice-floes of polar coasts and the Pal^ochrystic 

 sea leads to a speculation, in opposition to the views of geographers, 

 that " the Antarctic continent is nothing but an immense sheet of 

 ice, such as the PalEeochrystic sea would become if it were to inci'ease 

 in depth until it fastened to the bottom of the sea. Given a vast 

 sheet of ice wrapping the surface of a circum-polar sea, supposing 

 it to grow from winter cold and snow more rapidly than the melt- 

 ing of the water could remove it, the result would be that the ice- 

 sheet would in time cleave to the bottom of the sea, and become a 

 true glacier, although any portion of its bed was below the level of 

 the water." In favour of this hypothesis, is cited the southward 

 pointing of the southern continents and the gradual falling out of 

 land towards the South Pole. 



The distribution of existing glaciers, of former ones, and of glacial 

 drift, is shown by a map specially drawn for this purpose ; we notice 

 that no signs of any approach the tropics, while it is stated in the 

 text that L. Agassiz withdrew the suggestion that he once hazarded 

 about remains of glaciation in the Brazils. It is claimed for North 

 America that it shows the most extensive development of glaciation ; 

 that both in size and in their effects the glaciers were more massive 

 and powerful than those of Europe. The contrast here drawn will 

 be of interest to European readers. In Europe the Glacial Period 

 brought no general ice envelope except in its most northernmost 

 parts, but in North America quite other conditions prevailed : here 

 the ice lay as a continuous mass stretching down from the polar 

 regions to the central parts of the continent, overlapping the shores 

 for a great distance to the south along the coasts, and giving a con- 

 tinuous though irregular ice-front across the land from sea to sea. 

 This line as well as the direction of glacial striee over the north of 

 the continent is laid down on a second map. To this continuous 

 glacier face our author boldly ascribes the origin of numerous rock- 

 basins. The surface of this region is said to be worn into the 

 peculiarly uneven surface that glaciers alone can produce. Of the 

 myriad lakes that lie in the hollows of this uneven face the maps 

 show but a fraction. It is asserted that running water could never 

 carve a lake-basin in such rocks as occupy this region, while ice is 

 the only competent agent to do it. Great force must be given to the 

 argument drawn from the fact that rock-basins only exist in abun- 

 dance where glaciers have been at work, and in New England their 

 long axes lie so constantly in the direction of the flow of the ice 

 that it is said the Indians in thick weather used these lines of direc- 

 tion as a means of telling the position of the North. As far as 

 the thickness of the ice is concerned, it is indicated by the following 

 considerations : the ice is said to have completely covered Mount 

 Washington, which is about 5000 feet above the neighbouring table- 



