SNOW-MUSHROOMS AND CAHOTS 231 



the bumping of the sledges in passing over the 

 obstruction. 



Those persons to whom I spoke about cahots 

 had no doubt as to their origin. The transverse 

 ridges and furrows, they said, were only produced 

 when some obstruction made the sledge bump. This 

 was usually hardened snow — e.g., a drift blown 

 across a road. Sometimes, however, the sledge 

 started bumping on account of a hole in the road- 

 way beneath the snow. I decided, however, to 

 examine for myself the conditions of their forma- 

 tion, both with respect to the movements of the 

 sledge and the character of the surface over which 

 it travels. 



The motions of a sledge differ greatly from those 

 of a wheeled vehicle. The gliding runner meets 

 obstructions at a very slight, or grazing, angle, and 

 is very easily deflected from its course. If the 

 deflection be in a vertical plane, the sledge pitches 

 as a boat does. If the deflection be in a hori- 

 zontal plane, the sledge skids — i.e ., swings sideways, 

 and is then apt to capsize. Both these pernicious 

 tendencies are minimized in carts by the rotation 

 of the wheel. The skidding, or swinging, of the 

 sledge is responsible for the fact that the undula- 

 tions produced by it are broad, instead of being 

 as narrow as the runners. 



