268 R. Russell — On the Floiv of Rivers, S^c. 



previous winter, and consequently much less than the quantity that 

 ought to have been left as a residue from all the mass of the drift 

 carried away.^ Trom this it would appear that some drift can, in 

 a way not yet explained, change into fine silt, the blocks and frag- 

 ments of stone disappearing, and in some such way it might be 

 possible that the stony residue from the worm-formed mould might 

 also disappear, and thereby the thickness of soil be increased from 

 below ; however, against this idea still remains the facts stated as to 

 the thicknesses of the mould over the different kinds of sub -soils. 



From the above notice it appears that the writer cannot agree 

 with Mr. Darwin in believing that in the formation of the surface 

 mould " the whole operation is due to the digestive powers of the 

 common earthworm." But although Darwia disagrees with him in 

 this particular, yet all tJie observations of this eminent Naturalist go to 

 prove that in grass land chemico -fluvial denudation is stopped, unless, 

 indeed, part of the worm-formed earth is carried off by that denudent. 

 The latter, however, could scarcely be possible (save in some excep- 

 tional case), for if this agent so acted, it must reduce the quantity of 

 the worm-formed earth, which otherwise would be much more con- 

 siderable than at present. 



V. — On the Flow of Eivers anb the Measure of Eiver Sediments. 

 By E. Russell, Esq., of the Geological Survey of England and "Wales. 



THE importance of experiments and investigations such as those 

 recorded by the Eev. J. D. La Touche, in the Geological 

 Magazine for April, can hardly be over-estimated from a geological 

 point of view, and, if carried on in numerous districts and for a 

 sufficient length of time, would furnish data with which, and a basis 

 from which, future calculations as to the rate of denudation at 

 present going on over the land surface of the globe might be esti- 

 mated. For it cannot be denied that at present there is a laxness 

 in the method of computation as regards the rate and amount of 

 degradation both for past and present epochs which ill accords with 

 the ultimate end and aim of all scientific pursuits, viz., truth. Each 

 one taking a rate which seems most to confirm his own particular 



1 The river that flows from Lough Cooter County Galway, at the place now 

 called the " Devil's punch howl," a few miles southward of Gort, has gradually eaten 

 into an accumulation of Boulder-clay drift, until the drift chff over the vent, a natural 

 filter, is ahout 100 feet high. This drift is similar to the general Boulder-clay drift 

 of the central plain of Ireland, being boulders and fragments of Carboniferous lime- 

 stone with some of sandstone, contained in a clayey, slightly sandy matrix Yearly 

 this stream during floods, carries away a mass of the drift, yet when the water 

 is low, few or none of the boulders and fragments that apparently ought to have been 

 left as a residue of the drift can be seen, the river bed containing scarcely anything 

 else but angular cherty gravel. Some parts of the blocks and fragments may have 

 disappeared by abrasion, and the limestone may possibly dissolve and go away in 

 solution, but how have they disappeared so rapidly, and what has become of the pieces 

 of grits and sandstones ? The latter are not very numerous, yet there are many of 

 them, and how have they disappeared, as they could not have_ gone through the 

 filter, and they could scarcely have dissolved and gone off in solution ? 



