238 Organic Siliceous Remains. 



borings through the deposits, were made. The typical mud of 

 this class is generally of some shade of a dark grey-brown color, 

 having sometimes nearly the consistence of a very tremulous jelly, 

 but pasty to the touch. Some specimens of this, dried so as to be 

 so firm as to retain a moulded form, contracted to one tenth of its 

 volume when perfectly dried, nearly 50 per cent, of which was 

 estimated to be organic silica. While pieces of decaying wood, 

 leaves, mosses, etc., are found in this material, its carbonaceous 

 organic matter appears to have been to a great extent of algoid 

 origin. The waters of these lakes are generally colored by the 

 presence of organic matter in solution. 



The third class of deposits has not been observed in such abun- 

 dance as the other classes. In many cases it may have been formed 

 from material of the second class, as is suggested by the deposits 

 often shading off into each other in the same body of water. For 

 instance, in Macintosh Lake, some of the purest white material did 

 not come from the greatest depth of the water, but from the 

 vicinity of shallows, between an island and the mainland. A 

 gentle motion of the water from an exposed side of the lake is 

 produced by the wind over this flat, and the deposit alluded to is 

 immediately to the windward of the said flat. This suggests the 

 hypothesis that the change from the slimy mud to the purer siliceous 

 deposit may have been, at least partly, due to the solvent action 

 of the water on the decaying vegetable material. This solvent 

 action has been plainly demonstrated to exist by the analysis of 

 the waters of the lakes which supply the city of Halifax with 

 water, made by George Lawson, professor of Chemistry in Dal- 

 housie College and University. The waters of Long Lake, the 

 largest and highest of the series, was conducted for a time through 

 the lower Chain Lakes, in which there is a large deposit of diato - 

 maceous slime. The analysis gave 2.13 grains of organic matter 

 per gallon in the water of Long Lake, and 2.68 in that of the 

 lower Chain Lake. This shows that each gallon of water may 

 have dissolved out of the Chain Lakes about half a grain of 

 vegetable matter. 



Those lakes, so far as observed, which lie in the midst of granite 

 drift, and have clear water, have also purer silicious deposits, the 

 percentage of silica in the dried material approximating in some 

 ases to between 90 and 100. Folly Lake is an instance in which 



