218 



Forel (Faune profonde des lacs Suisses, p. 5) proposed to estimate the volume 

 of a lake by comparing it with a cone whose height is the maximum depth, and 

 whose base is the surface of the lake. Estimated in this way he found the cone 

 gave but .67 of the actual volume of Lake Geneva. A similar estimate for Tur- 

 key Lake will give us .024654 cubic miles, or considerably more than the actual 

 value. The average depth obtained by dividing the cubic contents by the surface 

 gives us 16.6 feet. All these measurements were made during the summer of 1895 

 when the lake was below the average height, so that 17 feet will probably be nearer 

 the average depth. It will be found that by another method Mr. Eidglev obtained 

 21 feet as the average depth. 



Over half the area contains water less than 10 feet dee^j. A reduction of 

 thirty feet below the present level would reduce the lake to a Y-shaped figure ex- 

 tending nearh' from end to end of the present lake. One of the horns of the Y 

 would extend to Crow's Bay, the other to Mineral Point. The base of the figure 

 would lie to the west of Black Stump Point. Between the horns of the Y we 

 should have a peninsula continuous with Morrison's Island, which is the last of a 

 series of islands left in the lake. During the ancient history of the lake the land 

 about Buttermilk Point was an island, and ridges of land east and west of this 

 formed the islands. One of these is seen in the illustration. The detailed descrip- 

 tion of the hydrography of the lake will be given in the map and Mr. Kdgley's 

 report. 



Relation of Water to Outflow and Evaporation. — Without any addi- 

 tion to the water of the lake the quantity now in the lake would be sufficient to 

 supply the present outlet for 26 years.* 



In other words, every cubic foot of water entering tlie lake will remain in it 

 on an average of twenty-six years, unless removed by evaporation. Ridgiev esti- 

 mates that the infiow from springs equals the outflow, yet the lake was observed 

 to fall on an average of one-quarter inch per day, rising of course during rains. 

 That the outflow will not account for the fail of the hike is sufficiently shown by 

 the fact that the calculated fall due to the outflow is l)ut .0016 inches per day. 

 (See Ridgley's report). Tlie remainder of the fall must be due to evaporation 

 and seepage, very largely to the former. Attempts were made to estimate the 

 amount of evajjoration from the surface, but they proved failures. It is self-evi- 

 dent that simply exposing water in an open dish will not answer the purpose of 

 estimating the amount of evaporation in the lake for the reason that water in a 

 shallow dish is heated to very diflferent degrees from the water of the lake. An 



'Based on Ridgley's and Juday's estimate of the outflow, and my estimate of the lake's 

 contents. 



