74- THE PROI'.LEM of LYNXHETS. 



In both cases the section shows the underlying hillside, 

 indicated by vertical lines, descending at a steady angle. 



Diagram C shows a section in accordance with the natural 

 theory, that lynchets are produced by differential hardness and 

 solubility, aided by the perennial passing of graminivorous 

 animals. There is very little accumulation of humus on the 

 ledge ; the slope of the lower bank, except immediately beneath 

 the treading feet, is much the same as that of the upper bank, 

 and the underlying hillside is itself marked by a step or terrace. 

 Of course, when advantage has been taken of a natural ledge, 

 and a tillage lynchet has been made upon it, the section ought 

 to resemble that shown by Diagram D, which is intermediate 

 between A or B on the one hand and C on the other. 



13. But another test can be brought to bear upon theory 

 besides the cutting of a lynchet, namely, a comparison of the 

 angle of the lynchet's lower slope with the angle of repose ; that 

 is, the angle with the horizon that loose materials assume after 

 being tipped. Immediately afterwards it may approach 45°, the 

 theoretical limit, especially if the material be wet and therefore en- 

 dowed with some adhesiveness. Subsequently the angle flattens. 



The angle made by Nature's tipping seen in the slope of a 

 talus is precisely similar, whether it is occasioned by the debris 

 of rocks, the crumbling of ruins, or the slope of hills. If the 

 tipping or the shedding of debris is carried on very slowly, or 

 has ceased altogether, the angle becomes in course of time 

 increasingly low. 



14. By practical engineers the angle of repose of ashes is 

 given as i to i, or 45°, in the first instance and as becoming 

 after a while \\ to i, or 33° 42 '; clean gravel and dry shingle as 

 31° 40', but, if wet, 11° 42'; and hard ivhitc clialk as from 45*^, 

 when freshly tipped, to 31° 40'. These angles, together with 

 many others that I have myself taken of tips in this neighbour- 

 hood, are set out on Diagram E. 



It would thus appear that any slope of apparently loose 

 materials that possesses a higher angle tiian 45° must be 

 assumed to be artificial, and that, if a slope is known to be due 



