332 THE BEAUTIES OF NATURE CHA: 
time if permitted, after a long cycle of years, 
to its first course. . 
In evidence of the vast quantity of sediment 
which rivers deposit, I may mention that the 
river-deposits at Calcutta are more than 400 
feet in thickness. 
In addition to temporary “ spates,’ due to 
heavy rain, most rivers are fuller at one time 
of year than another, our rivers, for instance, 
in winter, those of Switzerland, from the 
melting of the snow, in summer. The Nile 
commences to rise towards the beginning of 
July; from August to October it floods all the 
low lands, and early in November it sinks 
again. At its greatest height the volume of 
water sometimes reaches twenty times that 
when it is lowest, and yet perhaps not a 
drop of rain may have fallen. Though we 
now know that this annual variation is due 
to the melting of the snow and the fall of 
rain on the high lands of Central Africa, still 
when we consider that the phenomenon has 
been repeated annually for thousands of years 
it is impossible not to regard it with wonder. 
In fact Egypt itself may be said to be the 
bed of the Nile in flood time. 
