KHASI HILLS. 175 



But this water exerts its degrading forces not only on the surface 

 of the flats, or where, in rushing over the precipitous scarps it excavates 

 deep basins beneath, but it pours through the many fissures and clefts 

 in the sandstone and limestone, and springs from the solid face of 

 the rocks at different levels, tearing with it fragments of the hardest 

 masses, and precipitating them into the gorges below. 



The rapid degradation which these bills must undergo is well shown 

 by the vast amount of suspended matter, which 



Rapidity of degradation. 



is carried down by the streams issuing from them 

 during the rains. I have more than once seen streams which, in the 

 drier weather, were beautifully pellucid, so turbid and charged with 

 suspended matter, that a white card was invisible at the depth of one 

 inch and a half! that is, through a stratum of water of that thickness. 

 I have also measured the bulk of such sediment allowed to subside in 

 a carefully divided tube, and found it more than once to amount to one- 

 fifth of the total bulk, and in one case to very nearly one-third. In 

 all cases this sediment was a fine clayey sand. Taking these facts in 

 connection with the enormous fall of rain, it will be readily seen how 

 rapid must be the degradation and denudation of these hills. 



Nor is this without other proof also. Mr. Griffith, in his journal, 

 notices the fact of the steady retrogression of the Mawsmai falls, which 

 he calculates to have been at the rate of five feet in the year, and 

 he even proceeds to calculate on this supposition the lapse of time 

 which must have passed since these falls were originally at the general 

 face of the rocky scarp of the hills, estimating that it must have taken 

 5,700 years for the falls to have receded to their present position. ('a^ 

 But without attempting any estimate of this kind, which must inevi- 

 tably be erroneously based on such imperfect and unsatisfactory data, 

 the testimony of all the natives supports the conclusion that these falls 

 have continually receded, year after year. 



(a) Griffith's Private Journals, &c. — Calcutta, 1847. 



