276 On the Strata of the Dtidb Alluvium, [May, 



river. When the principal body is passed, the sediment becomes thicker, 

 and dropping over these falls, mixes with the sand of the horizontal run 

 beneath, forming first a single irregular mass on the upper side, whilst 

 the under is pretty irregular, and of a rounded form : in this at first 

 the sand predominates, the sediment continues dropping and adding to 

 the stone, until all the sand within reach has been sucked in, when the 

 formation ceases, and all the sediment that continues to fall on the same 

 spot, adds nothing to, but merely rests on the composition, and is washed 

 off by the next run of water, leaving a perfect stone. Six or eight 

 stones are very frequently formed in this manner, of different shapes 

 and varieties of composition, under the same fall, which is entirely re- 

 gulated by accident ; in some of these sand predominates, (specs. 10 

 and 11,) in others clay : again, the composition consists of nearly equal 

 portions of each. One fall may produce 10 or 12 stones separate, 

 which another run of water may from the sediment falling on a laver 

 of sand deposited since their formation unite, thus forming one stone, 

 (spec. 12,) the difference between the first formed and their cement 

 being very perceptible. The cement becomes set and as hard as dry 

 mortar in two hours after the mixture has taken place, and after three 

 days' exposure to the sun, they attain the substance of stone more or 

 less hard, according to the justness of the proportion of the composi- 

 tion ; these stones being generally round, are more frequently in motion 

 than any other substance, and is owing to mistaking them for natural 

 kankar, (I say natural, as I believe the substance to be kankar, of 

 mechanical formation, the same ingredients forming in my opinion 

 both,) that the term kankar shoals has been applied. 



Of the Sunken Trees. 



This dangerous obstacle to navigation is so well known from its 

 occurrence in almost all navigable rivers, whose banks are covered with 

 wood, that little need be said of it here. 



The trees have originally occupied a position on the verge of the 

 bank, which the stream having undermined, they have fallen into the 

 river, with a quantity of earth attached to the roots, the weight of 

 which firmly anchors them to the bottom, the head laving- with the 

 stream. In the Jamna any portion visible above the lowest levels is 

 cut off to the water's edge by the inhabitants of the nearest village, 

 leaving the bluff stumps of the large branches in the most dangerous 

 position possible, at average levels. In 1833, the whole of these be- 

 tween Agra and Allahabad were sought for and taken out, and by the 

 precautions then taken by the superintendant, it is next to impossible 

 that any other instances can occur for many years, as every tree with- 



