TTLOE — QTJATEBN-AEY aElVELS. 



61 



it to lower levels into the valleys. At page 124, Quart, Jonrn. 

 Geol. Soc. vol. xxiv., I described snch a flood, in Sind in the year 

 1866, when a rainfall of 24 inches occurred in ten honrs, laying all 

 the surface of the land under water, and moving very great weights 

 a considerable distance. The ancient river- deposits of the Thames 

 basin associated with this flood-borne detritus are generally covered 

 by an upper bed of well-rolled gravel, not exceeding 10 feet in thick- 

 ness. This bed is often only 3 or 4feet thick, and lies on the frequently 

 eroded surface of the stratified brick-earths and clays of the middle 

 part of the Thames Quaternary series. Even when for a short 

 distance this surface-bed contains few pebbles, there is no difficulty 

 in identifying it ; for it will soon be charged again with pebbles. 

 This thin upper coating of well-rolled pebbles, enc"'.osed often in a 

 stiff brown clay, but sometimes in sand or loess, extends from the 

 river-banks to near the tops of the hills over all the other parts 

 of the series of gravels, and often over the London clay and chalk ; 

 it covers a most extensive area, forming a marked contrast to 

 the middle series of laminated brick-earth, false-bedded sands, and 

 stratified clays, which are more confined to the low levels near 

 the rivers or brooks. This bed of upper clay and pebbles slopes 

 to the lower ground (I estimate on an average) at I in 260, and 

 falls therefore about 20 feet in a mile. It is washed over the 

 surface of the land smoothly, removing all abrupt heaps of gravel, 

 and leaving no greater irregularities of the surface in the London 

 basin than occasional low terraces. The smoothness and perfect 

 manner in wliich the gravel is deposited is shown by the fact that 

 the surface of the London clay or chalk is covered, notwithstanding 

 inequalities of the surface, by a bed only 25 feet thick over such a 

 laro-e district. 



Fig. 1. — Map of part of the course of the river Aire, Yorlcshire. 



RIVER AIRE YORKSHIRE 



Map of the course of the E-iver Aire, from Bindley to Castleford. The 

 letters refer to the hnes crossing the river, and are for refei*ence to the 

 longitudinal section (fig. 2) of the River Aire, or rather of a line sup- 

 posed to be drawn at each point of its course 8 feet above the full- 

 water-mark of tli3 river. This map has been accurately reduced by 

 the pentagraph from the one-inch Ordnance sheets. 



The river Aire rises near Malham Tarn, in Yorkshire, in the Car- 



