I 



n.] THE PEBBLES IN THE STEEET. 53 



hither along the surface of the ground, by primeval 

 hurricanes, ten times worse than those of the West 

 Indies, which certainly will roll a cannon a few yards, 

 but cannot, surely, roll a boulder stone a hundred 

 miles. 



Now, suppose that there was a force, an agent, 

 known luckily for you, not to you but known too 

 well to sailors and travellers ; a force which is at work 

 over the vast sheets of land at both the north and 

 south poles ; at work, too, on every high mountain 

 range in the world, and therefore a very common 

 natural force ; and suppose that this force would 

 explain all the facts, namely 



How the stones got here ; 



How they were scratched and rounded ; 



How they were imbedded in clay ; 

 because it is notoriously, and before men's eyes now, 

 carrying great stones hundreds of miles, and scratching 

 and rounding them also ; carrying vast deposits of 

 mud, too, and mixing up mud and stones just as we 

 see them in the brick-pits, Would not our common 

 sense have a right to try that explanation ? to suspect 

 that this force, which we do not see at work in Britain 

 now, may have been at work here ages since ? That 

 would at least be reasoning from the known to the 

 unknown. What state of things, then, do we find 

 among the highest mountains ; and over whole 

 countries which, though not lofty, lie far enough 

 north or south to be permanently covered with ice ? 



We find, first, an ice-cap or ice-sheet, fed by the 

 winter's snows, stretching over the higher land, and 

 crawling downward and outward by its own weight, 

 along the valleys, as glaciers. 



