R. M. Deeley — Disturbed Gravels. 



159 



margins of these areas, and that when crushing goes on the deposit 

 rises and raises ridges on the surface of the ground. We should then 

 have on the surface of the ground a complicated series of ridges with 

 numerous hollows between them. During periods of thaw the finer 

 material would he washed into these hollows. 



Fig. 1 shows diagrammatically how this process is supposed to 

 take place. A A is the ground-level and BB the water-level in the 

 gravel and sand. "When the frost reaches the water-level expansion 

 takes place and there is movement in the direction shown by the 

 arrows. Below the points marked D the gravel and sand rise and 

 ridges are raised on the ground surface ; when thawing occurs the 

 loose material of the ridges is washed into the hollows. We thus 

 have the material rising at DD and sinking areas at C C C. 

 Eventually troughs of rainwash form at the points C and gravel 

 waves below the ridges D. 



It is possible that when once lines of weakness had been formed 

 in the gravel below the surface, crushing generally goes on along 

 the same lines each winter, and that rainwash collects in the same 

 hollows each summer. A repetition of this process results in the 

 formation of waves of gravel separated by troughs of rainwash. 

 Much would depend upon the water-level in the gravel and the 

 direction of the water circulation in the gravel. It may be that 

 the waves and troughs tend to arrange themselves parallel with 

 the direction of the underground flow. 



If such an explanation be the true one, we should expect to find 

 such ridges and hollows on the surface of gravel deposits in Arctic 

 regions. Various patterns have been noticed on the surface of the 

 ground in high latitudes, and it would be well to examine them very 

 carefully. 



Any surface stones or flint implements resting on or near the 

 surface would, if the above theory be correct, get buried deep in 

 a deposit with which they are not contemporaneous. In some such 

 way flints have been buried five or six feet deep in deposits which 

 did not originally contain flints ; indeed, it has always seemed surprising 

 how foreign articles have managed to bury themselves so deeply even 

 in gravelly deposits. It is necessary in all cases to make sure that 

 flint implements are in undisturbed bedded gravels and sands ; for if 

 they are not they may have been introduced long after the deposit 

 was formed. 



