190 



PEOCEEDINGS OF THE GEOLOGICAL SOCIETr. 



takes place, of which I had a good example the last rains. The 

 Markunda river 12 miles east of Umballa, where it is crossed by 

 the Grand Trunk Eoad, had its deep channel too near the right 



Fig. 2. — Diagram Section of alluvial deposits. 



bank, which I was desirous of diverting by attaching brushwood 

 to a chain. In the next flood what was in the evening the 

 deepest channel was during the night raised about 3| feet, the 

 deep channel being forced more towards the centre. "When I came 

 to dig into this sand bank, all thrown up in one flood, I found over 

 an area of several hundred yards for the first 6 inches or so a dirty 

 sand, for the next 3 inches a comparatively clean coarse sand, with 

 a sharp line of demarcation above, and immediately below this a 

 fine loamy reddish clay, some 15 inches thick, without any admixture 

 of sand that I could observe, and underneath this again the same 

 dirty fine sand that covered the surface. These intermittences all 

 took place during the same flood of one night ; so these diff'erent de- 

 posits were not the work of years, but of hours*. With such va- 



* Where the Markunda is crossed by the Grand Trunk Eoad, at -J^ of a mile 

 back from the river the ground is 5^ feet below the river-banks on the east side ; 

 and a mile further on it is 13 feet below the bank, while on the west or Um- 

 balla side, \^ mile from the river, the land is 4^ feet below the river. 



This difference of fall on the two sides is owing to the line of road crossing 

 the gravel-fall of the country, which is some 3^ feet per mile in a rather oblique 

 direction. The surface velocity with a 5-feet flood passing down was 6 feet a 

 second. With high floods I found that the water held in suspension clay and 

 sand as follows : — 



Clay. Sand. 

 Flood 9-9 =10-75+47-5 =58-25 

 „ 7-3 =13-37+19-25=32-62 

 „ 7-6 =13-00+6-75 =19-76 

 „ 6-0 =ll-87-|-6-19 =1806 

 „ 6-4 =ll-65+5-56 =17-21 



Per cent, by weight 4-83 

 ,, 2-74 

 „ 1-65 

 „ 1-50 

 „ 1-43 



Mean 243 



These results were taken by only one set of experiments ; so no great depend- 

 ance can be placed in them ; but they show generally that the greater the flood 

 the greater the proportion of sand to the clay, and that the transporting power 

 increases at some quick ratio as the velocity increases. Professor Medlicot, I 

 believe, made the proportion of silt in suspension in the flood-water of the Solani, 

 which has a slope of some 5 feet in the mile, between 3 and 4 per cent. ; and I 

 made the Eatmao, which stream has a slope of 8 feet, to carry 5 per cent. ; while 

 the Puttri torrent, with a slope of 25 feet a mile, brought down 7 per cent, of 

 silt by weight, though the flood at the time was about 3 feet only. 



[Unless the cross section abuts on the slope of the stream it is impossible to 

 calculate the velocity or the transporting force of the water. — A. T.] 



