553 



THE POPULAR SCIENCE MONTHLY. 



as engraved illustrations in this volume. 

 The author also presents very fully the re- 

 sults of the labors of others, both in the 

 United States and in Canada, as Agassiz, 

 Dana, E. and C. H. Hitchcock, Newberry, Le 

 Conte, Lesley, White, Chamberlin, Salisbury, 

 Todd, Gilbert, McGee, Shaler, Davis, Stone, 

 Russell, Upham, A. and N. H. Winchell, 

 Claypole, Spencer, Whitney, Sir William and 

 G. M. Dawson, Bell, Chalmers, and many 

 more, often quoting from their reports and 

 memoirs, and reproducing their illustrations 

 and maps. The work is thus a compendium, 

 well brought up to date, of the already 

 voluminous literature of this wonderful geo- 

 logic winter of our globe. 



Glaciers now exist, as described in this 

 volume, on the Sierra Nevada, on Mount 

 Shasta, in the Selkirk Range, and in great 

 numbers and extent northward to Mount St. 

 Elias and Unalaska. In the chapter on the 

 glaciers of Greenland, a map shows the 

 route of Nordenskiold in 1883, and of Dr. 

 F. Nansen last year upon the ice-sheet that 

 covers its interior, extending in a vast mo- 

 notonous expanse which rises gradually to 

 elevations in its central portion six thousand 

 to ten thousand feet above the sea. The 

 further description of glaciers in other parts 

 of the world, and of the antarctic ice-sheet, 

 prepare the reader for the discussion of the 

 signs of former glaciation in the now tem- 

 perate regions of North America and Eu- 

 rope. 



The striation of the bed-rocks, the stri- 

 ated pebbles and bowlders of the drift, sec- 

 tions of till and of stratified drift and loess, 

 the characteristic topography of kames, ter- 

 minal moraines, and the oval hills of till 

 called drumlins, are very clearly described, 

 with excellent illustrations from photo- 

 graphs. The boundary of the glaciated area 

 from the Atlantic to the Mississippi is shown 

 in a series of six maps ; and a general map 

 showing the glacial geology of the United 

 States delineates, besides this southern limit 

 of the North American ice-sheet and drift, 

 the successive terminal moraines formed at 

 times of halt or readvance of the ice during 

 its retreat and final melting, the courses of 

 the glacial striae and transportation of bowl- 

 ders, the driftless area of southwestern Wis- 

 consin and portions of adjoining States, the 

 modified drift deposited in valleys of south- 



ward drainage from the ice-sheet, and the 

 boundary of the glacial Lake Agassiz which 

 was held in the basin of the Red River of 

 the North and of Lake Winnipeg by the 

 barrier of the ice while it was being melted 

 away. 



Important changes in the drainage of the 

 country, caused by the ice-sheet and its drift 

 deposits, are noticed in considerable detail. 

 In the same way that Lake Agassiz was 

 formed, outflowing by the glacial River 

 Warren along the course of the Minnesota 

 and Mississippi Rivers, the Great Lakes of 

 the St. Lawrence were held by the receding 

 ice-barrier at levels much higher than now, 

 similarly outflowing over the lowest points 

 in their southern water-shed to the Missis- 

 sippi ; and these ancient lake-levels are still 

 found distinctly marked by beach ridges and 

 deltas of gravel and sand. Another very 

 interesting glacial lake was formed in the 

 basin of the Ohio River by the temporary 

 dam of the ice-sheet, which at its time of 

 maximum area extended across this river at 

 Cincinnati, carrying its morainic drift into 

 the northern edge of Kentucky. "These 

 glacial deposits south of the Ohio," accord- 

 ing to Prof. Wright's observations, "are 

 such as to make it certain that the front of 

 the continental glacier itself pushed, at some 

 points, seven or eight miles beyond the Ohio 

 River; and it is altogether probable that 

 for a distance of fifty miles (or completely 

 around the eastern, northern, and western 

 sides of the Kentucky peninsula formed by 

 the great bend of the river) the ice came 

 down to the trough of the Ohio, and crossed 

 it So as completely to choke the channel and 

 form a glacial dam high enough to raise the 

 level of the water five hundred and fifty feet 

 — this being the height of the water-shed to 

 the south." Traces of the former existence 

 of this Lake Ohio are found along a distance 

 of about four hundred miles in the valleys of 

 the Ohio, Alleghany, and Monongahela Riv- 

 ers and their tributaries. At the present 

 time the abundant lakes, and the waterfalls 

 on streams, throughout the glaciated area, 

 so remarkably contrasted with their general 

 absence farther south, are due to irregulari- 

 ties in the deposition of the drift and to its 

 obstructions of the preglacial drainage. 



A chapter is devoted to the flight of 

 plants and animals during the Glacial pe- 



