282 Proceedings of the Royal Physical Society. 



geology. Since each flood tends to deposit stones, etc., in 

 graduated sizes upon the accreting sides of stream-channels, 

 it follows that if the flood-force of water be habitually great, 

 the basement stones of the gravel beds formed by it will be 

 proportionally large (Fig. 10), the gradation from these up 





<3 



R[_jy/ / Li^H Jl^j]^^ — Id^Fgel- over stream 



Fig. 10. 

 Section of River Gravel (Whickliope Burn, North Tyne), 



Gra., Gravel, coarse in lower part ; R, rock, quarried. 

 Note. — This gravel-bed may be viewed as sub-torrential. 



into alluvium proportionally extended, and the gravel-bed 

 thick in consequence. The average thickness of gravel is 

 determined by the average height of flood. When, therefore, 

 we seek to know something of the bodies and force of water 

 that deposited ancient river-gravels, we may expect to find 

 it registered — (1.) in the average thickness of gravel, and (2.) 

 in the size of the blocks deposited towards its base.* Floods 

 of variable range will register the fact in a greater inter- 

 weaving of coarse deposits with finer, and in more contem- 

 poraneous erosion ; and any floods of extraordinary and 



a series of articles now current in the Geological Magazine declares that "the 

 two kinds of work " — denudation and deposit — are " absolutely antagonistic," 

 in the sense that a stream " cannot at the same time act as a scouring agent, 

 and as a depositing one" {Geol. Mag., 1882, p. 442). The " Evidences of a 

 Great Post-Glacial Flood," it would seem, are a little disconnected from much 

 study of the effects of smaller ones. 



* The largest blocks of all, of course, are those which the river has never 

 been able to shift, but has only let down time after time as the valley 

 deepened. These need have no reference to the force of the stream. The 

 arrangement of recent torrential deposits can best be studied now-a-days, in 

 this country, in the steep head waters of rivers. 



