42 Nature of Aquatic Environment 



being plant and animal remains. From all these non- 

 living substances the water tends to free itself: The 

 lighter organic substances (that are not decomposed 

 and redissclved) are cast on shore ; the heavier mineral 

 substances settle to the bottom. The rate of settling 

 is dependent on the rate of movement of the water and 

 on the specific gravity and size of the particles. Fall 

 Creek at Ithaca gives a graphic illustration of the carry- 

 ing power of the current. In the last mile of its course, 

 included between the Cornell University Campus and 

 Cayuga Lake, it slows down gradually from a sheer 

 descent of 78 ft. at the beautiful Ithaca Fall to a scarcely 

 perceptible current at the mouth. It carries huge 

 blocks of stone over the fall and drops them at its foot. 

 It strews lesser blocks of stone along its bed for a quar- 

 ter of a mile to a point where the surface ceases to break 

 in rifrles at low water. There it deposits gravel, and 

 farther along, beds and bars of sand, some of which 

 shift position with each flood rise, and consequent 

 acceleration. It spreads broad sheets of silt about its 

 mouth and its residual burden of finer silt and clay it 

 carries out into the lake. The lake acts as a settling 

 basin. Flood waters that flow in turbid, pass out 

 clear. 



Whipple has given the following figures for rate of 

 settling as determined by size, specific gravity and form 

 being constant: 



Velocity of particles jailing through water 

 Diameter 1. inch, falls 100. feet per minute. 



i I << 11 O It'll II 



.01 " " .15 " " 



.001 " " .0015 " " 



tt a i 1 _. i 1 ti it 



.OOOI .OOOOI5 



Suspended mineral matters are, as a rule, highly 

 insoluble. Instead of promoting, they lessen the 

 productivity of the water by shutting out the light. 



