7o8 THE POPULAR SCIENCE MONTHLY. 



vast ice weiclits from one end of the world to the other? On all the 

 mountains of New England there are sea-lines at elevations of 2,000 

 and 3,000 feet, and Lyell himself has recorded the facts. When 

 the ocean was that deep over Boston, there were no continents in the 

 northern hemisphere. Undoubtedly the height and direction of moun- 

 tain-ranges, the trending of sea-shores, and the course of ocean cur- 

 rents, have much to do with local climates. But, instead of the rela- 

 tive quantity or location of land and sea having any agency in pro- 

 ducing the glacial periods, it is these periods which produce the land 

 and the sea. 



So much for the causes and conditions which pertain to the geog- 

 raphy of the present and the future. When, now, we turn back a few 

 of the leaves which tell of the past condition of our planet, we imme- 

 diately see that the same causes have been at work in recent geologi- 

 cal times on a much more extensive scale in fact, that they have 

 been the chief agents in composing and modifying the present surface 

 of the earth outside of the tropics. Over all the northern portions of 

 Eurojie, Asia, and North America, are found the unmistakable evi- 

 dences of extensive and recent ice-work. Bowlders of every size, 

 some worn and some angular, are scattered in immense quantities 

 over all the country, on the hills, on the plains, in places where the 

 only possible explanation is that they were lifted up, carried, and 

 dropped, just where they are found; and the great iceberg was the 

 carrier. T!ie face of the rock-beds, wherever brought to view, in the 

 valleys or on the moimtains, is almost always found to be grovind or 

 polished, and, over that, grooved and furrowed with nearly parallel 

 scratches. The Alpine glaciers are doing exactly the same work to- 

 day. Erratic blocks of foreign origin, and sometimes of enormous 

 dimensions, are frequently found perched on the very tops of hills, or 

 stranded high up the mountain-sides ; and the quarries from which 

 they came are invariably found to the northward, sometimes fifty or 

 even a hundred miles. It is argued that nothing but polar glaciers 

 could thus have moved them in uniformly meridional lines. The 

 scrapings of grounding ice-floes, the marks of ancient sea-shores, and 

 marine relics and shells, are found at elevations of several thousand 

 feet above the present ocean-level. There is no escaping the conclu-_ 

 sionthat the northern continents have been, in not remote ages, deeply 

 submerged beneath an ice-laden sea ; and that the entire polar and 

 north temperate regions, extending in some places south of the for- 

 tieth parallel of latitude, have been capped with one massive covering 

 of ice of great thickness. Precisely the same evidences are found in 

 South America, and, according to Agassiz, even much nearer the equa- 

 tor than in North Amei'ica. We have again to search our astronomy 

 for causes many times more powerful than any thing we have yet 

 found, for differences of polar temperatures. 



The earth is made to revolve in an orbit drawn out of the circular 



