[whittaker] bottom DEPOSITS OF McKAY LAKE 149 



pletely covered the surface of the lake so that it was safe until spring. 

 Immediately after the breakup of the ice on the 25th of April, the 

 sedimentation pans were visited. It was found that the rope had 

 been decomposed and while the ends were recovered several times by 

 a boat hook, yet they immediately parted again, and in consequence 

 the pans could not be located. 



In the winter of 1919-20, additional data were secured; the same 

 method as above was again employed except that a small covered 

 copper wire was used which proved satisfactory. Steel wire was used 

 in the beginning, but it was found that its resilience caused a tension 

 on the wire close to the pan which tended ultimately to overturn it. 

 The copper wire proved quite satisfactory. 



As before it was found that no appreciable sediment was deposited 

 during the winter months. In the spring while the ice was still solid 

 in the middle of the lake a large amount of water always collects upon 

 it more especially close to shore. This is derived partly from melted 

 ice in the lake itself, but to a large extent represents drainage down 

 from the surrounding land which does not pass off through the regular 

 outlet of the lake. This water which comes down by many minute 

 rills brings down a considerable quantity of fine rock fragments, clay 

 particles, etc. This spreads out over the ice which is covered by the 

 water. As might be expected there was a thick bed of coarse material 

 close to shore and the finer material farther out. In all probability 

 this material, upon the breaking up of the ice, is scattered over a 

 very large area of the lake as the fragments of ice are moved by the 

 winds. An analysis of the finer material shows definitely no trace 

 of calcareous sediments. Close to shore this layer was about 1" in 

 thickness, gradually thinning out to an impalpable thickness, within 

 about forty feet of the shore. It seems entirely probable that material 

 of this nature accumulating in spring, has contributed to a con- 

 siderable extent in the production of seasonal deposits throughout 

 the lake. A pan placed in the middle of the lake examined shortly 

 after the ice had completely broken up showed a minute but per- 

 ceptible trace of sediment, approximately h millimetre in thickness. 

 This showed only a minute trace of lime. 



A sample of this mud which had come down upon the ice was 

 kept in the office in a loosely closed jar covered with water. In the 

 course of two months a layer of reddish brown flocculent material 

 appeared upon the surface of the mud. This layer was about 2 mm. 

 thick. Upon examination with a microscope it was found to consist 

 entirely of algae. This suggested a resemblance to the jelly-like 

 material in the deeper part of the lake. During this last summer 



