Cause of Horse-shoe Bends in Rivers is unequal Ram-fall. 459 



I hope to show that rivers and lakes now occupy valleys and hollows formed 

 when the physical and atmospheric conditions of our island were very different 

 from those it now presents. 



Ancient rivers may have had many hundred times as much destructive effect 

 on the surface of the earth, for erosive force increases in the fourth power of the 

 velocity, and may have eroded the surface of the earth as much in former times 

 in one year as they now do in 1,000, in cases where rocks were made to slide 

 on clay by excessive supply of percolated water. 



I must ask you to assume what I have demonstrated many years since in 

 another place, that all valleys, without exception, are enormously large, com- 

 pared with the present rivers and brooks occupying them, and that the present 

 size is the proof of the former rainfall or snowfall. This fact is visible to every- 

 one in their walks or journeys, and the only inference from it is, that in the. 

 period just before man appeared, when the valleys were enlarged to their present 

 size, the rainfall or snowfall was at least fifteen times as much as at present. 



Figure 31 shows that rivers enlarge their channel on one side, the concave,, 

 and silt up on the convex side. The consequence of unequal rainfall is this 

 movement of river channels in horse-shoe bends. 



Some of these valleys were excavated in a very cold or glacial period by the 

 action of enormous quantities of iee. Other valleys were excavated or en- 

 larged by the action of ancient enormous rivers and springs of great power, in 

 what I have termed the pluvial period. 



Fig. 31 shows a case of a river changing its course in a flood 150 feet. 



(27) 



FIG; 51 . RUTMOO HIVER. 



T5Cf^ Movement of xiirez channel/ in. one fh&d 



WiaGi,&A,M<5(rftetl 



Horn. SirP. Cccuitey jxnje. sz LSSO 

 A 



Figure 25 is a specimen of the action of springs, and represents the hills near 

 Folkestone : at the present time most of these springs are very small. 



These ancient streams were fed all over the globe by such rains as fall only 

 in few places at the present time. In the Nile there are no tributaries at pre- 

 sent falling into it for 1,000 miles from the delta, but there are dry valleys 

 opening into the great Nile valley of enormous size, so that 300 inches of rain 

 falling in the now dry climate of Egypt, would be carried away by the river, 

 not without inconvenience, but without much difficulty. 



The Cyrena fluvialis, now living in the Nile, was also found 120 feet above 

 the present water level, at Silsilis, by A. Harris, showing that in floods in the 

 pluvial period (which I consider that of man) the whole valley of the Nile, 

 wide as it is, must have been charged with water up to 120 feet above the 

 present flood level. 



I think 300 inches of rain is the smallest quantity that could have fallen in a 

 year, when the great masses of the Thames Valley gravels were deposited on 

 ground where the present streams cannot move the old deposits. 



That the present rainfall has not sufficient force to excavate new brooks and 

 rivers in the London or any ordinary flat or alluvial district, I think will be ad- 

 mitted by all. There is no case of this kind known since the historical period, 

 in the Thames Valley. 



If I can prove the truth of the new law,* that with twenty-seven times the 



* I first reduced this law to an equation from observation, and illustrated it by a diagram, 

 in 1871. 



