ite) BOTANICAL GAZETTE [JULY 
It will be seen that the accumulation of vegetable matter has 
been sufficient to cause the lake basin to be filled with a layer of 
peat of considerable depth. The deeper strata have been reduced 
by humification, largely to the form of a black humus, a semi- 
liquid muck. The fineness of grain and the peculiarly soft con- 
sistency of it suggest that it is in part made up of the remains of 
algae, and in part a filling from the border of the lake, spread 
over the bottom. The upper strata are lighter in color, and very 
fibrous, loosely felted in structure, and have a matted appearance. 
As the island is sounded through from top to bottom, the samples 
brought up show a progressive change in color from light to darker 
shades, and in texture from coarse and loose to fine and more 
compact peat always saturated with water. In some places this 
sequence is repeated, that is, below the peat muck occurs a second 
fibrous brown layer followed by muck or clay. The escape of 
gases is very noticeable during the test borings, and also the stain- 
ing of the brass peat sampler to a bluish-purple bronze, indicating 
the presence of a gas like hydrogen bisulphide. Only a small de- 
posit of shell marl has thus far been found underlying the peat 
substratum in places. The Characeae and Cyanophyceae con- 
cerned with this process (10) are not abundant enough to be con- 
sidered as agents in the aggradation of the basin. The lake bottom 
is of clay and in places somewhat sandy. The thickness of the 
deposit of peat in this morainal depression indicates, therefore, 
that the vegetation must have obtained an early foothold. 
The chemical analysis of the substratum 
The drainage of the bog island is merely that due to seepage 
through the porous peat. Ordinarily very little water passes 
either into or out of the bog island, except at such times when the 
water level of the lake fluctuates with extremes in precipitation 
or from interference in drainage. Even then the seepage is not 
rapid. The amount of salts dissolved in the lake water which is 
retained by absorption in the humus soils along the margin of the 
bog island is relatively small. The analyses show a total mineral 
content of 4 and 9 parts per hundred for the central and marginal 
zones respectively. Average samples of the air-dried peat taken 
