Organic Siliceous Remains. 237 



These deposits may be roughly classified as follows : — 



First, earthy muds. 



Secondly, black or brownish slimy muds. 



Thirdly, whitish siliceous muds, consisting nearly entirely of the 

 cell-walls of the diatomaceee and the spicules of fresh-water sponges, 

 which are found to be present in classes first and second also, 

 although in less comparative abundance. 



These three classes, of course, shade off into each other with- 

 out any distinct line of demarkation. 



In the first class there is a variable quantity of fine sand or 

 clay introduced in times of freshets when the water becomes dis- 

 colored from the earthy matter borne into it. Deposits of this 

 class abound in lakes into which large streams that readily be- 

 come turbid flow ; and they form more rapidly, it is presumed, 

 than those of the other classes. Soundings in the upper portions 

 of the Lochaber, G-arden of Eden, Forbes, Ainslie and Grand 

 Lakes, for instance, bring up material of this class, all abounding 

 to some extent with diatom valves and sponge spicules. The 

 depths of thrse accumulations our primitive boring apparatus 

 would not allow us to fathom. 



The second class of deposits is found in abundance in lakes fed 

 by small streams in the forest. In Calder and MacKay Lakes, 

 Pictou County, the former being a full mile in length, the water in 

 no place appears to be over 9 or 10 feet in depth, the average 

 being 5 or 6 feet. In the central portions of these ponds a pole 

 was driven down by the hand from a raft to the depth of 20 feet 

 without striking hard bottom. ^Nearer the margin, the borer 

 after passing through this deposit, generally took up a stiff clay, 

 which has also been found underlying some peat swamps in the 

 neighborhood. In some of these swamps analysis has shown a 

 large percentage of the incombustible residue to be composed of 

 diatomaceous and sponge remains, thus demonstrating their lacus- 

 trine origin. When the hard bottom of the above-named and 

 other lakes was found to be undulating, the light slimy diatoma- 

 ceous mud was found to be deepest in the depressions, — the mud 

 surface being more conformable to the surface of the water than 

 to the surface of its bed. In JMacLean Lake, less extensive but 

 nearly 30 feet deep, the same characters of the bed of the deposit 

 were observed. In most of the other lakes, soundings, but no 



