THE POLAR GLACIERS. 29 



view, in the valleys or on the mountains, is almost always found 

 to be ground 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 moun- 

 tain-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- 

 sion that 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 fortieth 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 equator than in North America. 

 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 form by the combined attractions of the other planets, 

 Jupiter carrying the controlling influence. When the average 

 of all these forces for long periods is more in one direction than 

 in another, our planet is drawn away from the sun on that side. 

 Now it must occasionally happen, with the various periods of 

 revolution of the planets, that they will unite at times to produce 

 extreme irregularities. The present difference between the 

 nearest and farthest distance of the sun from us is 3,200,000 

 miles. It is found, by calculating back the planetary orbits and 

 conjunctions, that this focal distance has been as much as 14,000,- 

 000 miles. There was at such a time, an excess of thirty-nine 

 winter days during each year of the great secular winter of either 

 pole. This exceptionally high eccentricity occurred, according to 



