594 THE ICE AGE IN NORTH AMEBIC A. 



merited together by infiltrations of lime and iron. Down 

 the stream the stratum of peat rises to a higher level, so as 

 eventually to come in contact with the first band of stratified 

 material just mentioned, the intervening till gradually thin- 

 ning oat between them. The appearance is that of a saucer- 

 shaped deposit of peat such as would have formed in a ket- 

 tle-hole, and which was subsequently filled and covered with 

 the advance of the glacier. 



That the facts indicate a somewhat prolonged interval 

 between the first advance of the ice over the immediate re- 

 gion and the second, can not, therefore, well be denied, for 

 the peat is clearly enough between two glacial deposits. But 

 it may well be questioned whether an interval of two or three 

 centuries wo aid not suffice for the accumulation of the peat 

 described ; for it will be observed that it seems to have oc- 

 curred in a large kettle-hole in which the vegetable matter 

 naturally gravitated toward the center and is much deeper 

 there than near the edges. It is not therefore allowable 

 to take the extreme thickness of peat as the measure of the 

 amount of accumulation during the interglacial period. 



As to the rapidity with which peat may accumulate in 

 favorable circumstances, we can do no better than transfer 

 a recent discussion of the subject from the pen of the veteran 

 botanist, Leo Lesquereux, contributed to the " Annual Report 

 of the Pennsylvania Geological Survey for 1885 " : * 



Two conditions are necessary for the origin and growth 

 of peat — water either stagnant in basins, lakes, pools, etc., or 

 water abundantly supplied by a boggy atmosphere, increased 

 by dense forest-growth. 



Pools of stagnant water, when not exposed to periodical 

 drying up, are invaded by a peculiar vegetation : first, mostly 

 composed of confervce, simple, thread-like plants, of various 

 color and of prodigious activity of growth, mixed with a mass 

 of infusoria, animalcules, and microscopic plants, which, partly 

 decomposed, partly continuing the floating vegetation, soon 



* Pages 106, 107, 113, 114. 



