[TYRRELL] THE GOLD OF THE KLONDIKE 41 
all the way. It had been originally vertical throughout; but the creep 
of the upper softer portion of the schists which enclosed it had turned it 
over so that its upper portion assumed a horizontal attitude. 
This creep has a considerable influence on the formation of Placer 
deposits, as it tends to constantly move the loosened soil and earth 
down from the hills into the bottoms of the valleys. 
But the principal agent in the transportation of the loosened rock, 
and also in its concentration, is water flowing on the surface, either in 
minute rivulets or in larger streams. 
After a heavy fall of rain little rills are formed all over the ground, 
and these flow downwards, carrying a load of mud with them, and 
gradually join together into larger streams, and finally into brooks and 
rivers. As they become larger with a constant slope they increase in 
velocity and consequently have greater carrying power. 
*The following table gives the carrying power of a stream as exerted 
on quartz or rock of similar weight:— 



Velocity of Current. Size of material moved. 
3 inches per second — 1/6 mile an hour. Fine clay and silt. 
6 “ “ “ — 11 7e “ “ “ Fine sand. 
1 foot x Te =O ach eo Pebbles + inch in diameter. 
2 feet « “ — 1 z 33 “ “ “ “ 1 “ a“ “ 
9. 82 “ “ “ —— 1 À 9 “ “ “ “ 2 “ « “ 
« « « RARE ts & « « € « “ “ 
3-46 — 2-3 3 
4 “ “ “ —- 9 £ 7 “ “ “ “ 4 “ “ “ 
7 « « « PEN « « « « = & “ “ 
4-47 = 3 5 
« « (3 NAC; “ € « “ « “cc « 
4-90 — 83503 6 
€ « « « -2 « « ts « « « « 
5-29 — 13:10 7 
5 z 65 “ [12 [1 — 3 s 9 “ “ “ “ S “ “ “ 
6 “ « € == 4 “ “ “ “ 9 “ “ “ / 

With rocks of equal specific gravity the carrying power of a stream 
varies according to the square of the diameter of the pebbles; or the vol- 
ume of the pebbles which can be carried by a stream increases in the 
sixth power of its velocity; that is if the velocity is doubled, the dia- 
meter of a pebble which can be carried is increased four times, and the 
volume sixty four times. Conversely when the current is reduced one 
half, the volume of a pebble (weight being equal) is reduced sixty four 
times. 
Thus a very slight increase in velocity greatly increases the carry- 
ing power of a stream. For instance, a stream flowing at one mile an 
hour has power to transport particles of a certain size, and if that stream 
*Rivers of North America. By I. C. Russell. New York,1909, pp. 18-19 
