62 SCRATCHES AND GROOVES ON ROCKS. [CHAP. IV. 



trees, and the soil in which they are rooted. Some of these 

 masses have slid two or three miles, with an average breadth of 

 a quarter of a mile ; and so large are the rocky fragments, that I 

 found some of them, which came down in the Willey Slide, to 

 measure from fourteen to twenty feet in diameter. I also ascer- 

 trined that the steep slopes of bare rock over which they had 

 passed, were inclined, in some instances, at angles of twenty to 

 thirty degrees with the horizon. After clambering up more than 

 400 feet above the level of the Saco, on its right bank, I reached 

 a space of naked rock, fifteen feet square, over which my guide, 

 the elder Crawford, told me that the whole contents of the Willey 

 Slide had swept in 1826 ; which was indeed evident, for it lay 

 in the direct line of the great trench cut through the forest above 

 and below. 



There is a small cataract at the spot, where a dyke of basalt 

 and greenstone, four or five feet wide, traverses the granite, all 

 the rocks being smoothed on the surface, and marked with some 

 irregular and short scratches and grooves ; but not such as re 

 semble in continuity, straightness, or parallelism, those produced 

 by a glacier, where hard stones, which grate along the bottom, 

 have been firmly fixed in a heavy mass of ice, so that they can 

 not be deflected from a rectilinear course. 



I am aware that glaciers and icebergs are not the only means 

 by which the grooving and polishing of the faces of rocks may 

 be caused ; for similar effects may arise on the sides of fissures 

 where stony masses have been rent asunder, and moved upward 

 and downward, or made to vibrate during earthquakes, so that 

 the opposite walls are rubbed against each other. But we can 

 not attribute to this cause the superficial markings now commonly 

 referred to glacial action in Europe and North America ; and 

 what I saw at the Willey Slide, and other places in the White 

 Mountains, convinced me that a semi-fluid mass of mud and 

 stones must always have too much freedom of motion, and is too 

 easily turned aside by every obstacle and inequality in the shape 

 of the rocky floor, to enable it to sculpture out long and straight 

 furrows. 



From the Willey Slide we continued our way along the bot- 



