TITLES AND ABSTRACTS OF PAPERS 139 



who have considered related problems, and also with the hope that others 

 may be interested in undertaking similar studies at the same time, and thus 

 furnish checks on the results from different parts of the country. 



The Bottom and how it reached its present Condition 



When the ice retreated from the lake basin it doubtless left a bottom of 

 sandstone, till, sand, boulders, gravel, and clay. Wave and current action in 

 the deeper portions of the lake have apparently been able to accomplish little 

 or no erosion. Deposition has been the dominant physical process. To what 

 extent small, deep holes may have existed and been filled is unknown. Tins 

 is one of the facts to be determined. At present it seems probable that in tlie 

 main part of the area below a depth of 60 feet the bottom is a layer of mud 

 jind marl, comparatively uniform in thickness, of which we have but one 

 analysis,^ as follows: 



Loss of H2O at 105 degrees 1.29 



Loss on ignition (organic matter and GO2) 41.99 



Si02 15.85 



Fe^O, + ALO3 2.51 



CaO , 33.21 



MgO 2.16 



Na^O 0.95 



K2O 0.34 



SOa 1.37 



Total 99.67 



The amount of CO2 necessary to satisfy the CaO and MgO is 15.77 per cent, 

 which would leave 26.22 per cent as organic matter. 



This marl and mud mixture reached its present position by deposition of 

 material carried in by winds and streams, and that brought into suspension 

 by wave action in the more shallow portions of the lake and transported by 

 current ; by deposition of carbonates abstracted from the water by the abundant 

 organisms; and is also, in some considerable part, made up of the decaying 

 remains of the various forms of life which have existed In the water. Whether 

 any of the marl has been removed by solution is not known, but evidence for 

 tins nuist, of course, be sought. 



Determination of Amount of Sediment deposited 



It is proposed to make determinations in many places ; if possible, in some 

 manner by which sections or borings, complete and uniform from top to 

 bottom, can be taken out, dried, and weighed. The various portions will be 

 examined microscopically and chemically. When it is stated that the material 

 varies from a soft ooze at the top to the consistency of a .stiff clay at greater 

 depths, it is evident that it is not going to be easy to get satisfactory borings. 

 Any suggestions that will lielp to accomplish this will be most gratefully 

 received. 



A. and Jiulav <'. P.ir.ue : ^^'is. Cool, and Xa(. TTisl. Survey, T'.nll. xxii, p. 1' 



