SNOW-MUSHROOMS AND CAHOTS 245 



in the pull of the cord and, almost simultaneously, 

 a change in the sound made by the sledge. The 

 rattling over dry gravel had given place to a 

 muffled note, and the prow of the sledge had begun 

 to rise and fall. On turning to watch the sledge 

 the cause of this was immediately apparent. The 

 level of slightly damp, coarse sand had been 

 reached, and the pressure of the sledge soon 

 welded into a coherent mass the travelling mound 

 of material in front. The sledge then rode over 

 the obstruction, which after its passage was found 

 to be perfectly incorporated with the road-bed, 

 forming a gentle convexity of the surface. The 

 sledge at once began again to scoop up more 

 material and drive it in front. Presently it over- 

 rode the new obstruction, and a second wave-crest 

 was thus formed. 



The undulations increased very rapidly in ampli- 

 tude, not only when the sledge was drawn back- 

 wards and forwards but also when drawn only in 

 one direction. The undulations were symmetrical 

 in profile, and similar in appearance and steepness 

 to the cahots of the quarry track. No appreciable 

 inequality was present to originate them, the speed 

 of the sledge throughout was only that of a very 

 slow walk — i.e., about 2\ miles per hour — and the 

 pull was as steady as I could keep it. The 



10 



