215 



These figures do not claim any great degree of accuracy; they simply help 

 to form an estimate of the length of time it would take both the outflow and 

 evaporation together to empty the lake. But while it would take both the out- 

 flow and the evaporation fourteen years to empty the lake, one-fourteenth does 

 not express the per cent, of the water of the lake changed annually under present 

 conditions. Since the vertical reduction is the same whether the surface is large 

 or small, it is evident that a much larger amount would be evaporated while the 

 surface is large. In reality, if a bulk were to be taken from the lake equal to the 

 outflow, plus the evaporation over the present area, about six years would be suf- 

 ficient to empty the lake, or, to put it in other words, during average years every 

 cubic foot of water entering the lake remains on an average six years. During 

 very wet seasons the amount of loss may reach a much larger proportion of the 

 whole contents. 



Constancy of Turkey Lake as a Unit of ICnvironment. — From the 

 preceding chajiter it must be evident that the conditions in the lake, from month 

 to month and from year to year are but little changed, that the conditions, as far 

 as the water is concerned, are remarkably constant, especially if we compare these 

 conditions to those obtaining in tlie lower courses of such rivers as the Wabash or 

 the Illinois. 



In the early part of this century a dam was built across the mouth of the 

 outlet forming an effective barrier to the ingress of fishes from below. The lakes 

 being at the heatl waters, nothing has entered it from above. A few forms were 

 planted in recent years by Col. Lilly of Indianapolis. 



The level of the lake was changed by the building of the dam, and as late as 

 1840 trees were standing in water six to seven feet deep. Many of the stumps 

 still remain. Their location and the effect of the dam upon the lake will be dis- 

 cussed elsewhere. 



works consulted. 



A(jag>iiz, .1. Hydrographic Sketch of Lake Titioaca. Proc. Am. Acad. Art 

 and Sci, XT, 11, 283-292; 1876. 



Agassiz, L. Lake Superior. 



Belloc, M. E. Les lacs de Cailiaouas et ceu.x de la region des Gourgs-Blancs 

 et de Cladabide. Assoc. Francaise 9 Aout, 1893. 



Beltor, M. E. Nouvelles recherches lacustres feites an Port de Venasquedans 

 le haut Aragon et dans la haute Catalogue. Assoc. Francaise 9 Aout, 1893. 



Comatoc, C. B. Professional papers corps of engineers U. S. A., No. 24, 

 Primary triangulations U. S. lake survey. Washington, 1882. 



