460 A POPULAR EXPOSITION OF THE 
higher latitudes and Alpine elevations in which they still prevail. No 
strong or abrupt lines of demarcation can thus be drawn between the 
close of the Cainozoic Age and the dawn of the existing state of things 
The one period merged slowly into the other ; and certain life-forms, 
indeed, appear to have existed throughout all the changes which occa- 
sioned and accompanied the general deposition of the Drift. 
Recent Deposits :—These comprise various formations, of limited 
thickness and extent, produced by causes now, or recently, in action at 
the localities in which these deposits occur. The principal consist of : 
Shell marl, calcareous tufa, bog iron ore, ochres, and peat. Shell marl 
is a soft calcareous deposit made up largely of the minute shells of cer- 
tain species of planorbis, cyclas, and other fresh-water mollusks. It 
occurs at the bottom of almost all our lakes, ponds, andswamps; and 
sometimes forms near the margin of these, a bed of several feet in 
thickness. This lies usually at a short depth beneath the surface 
of the ground. It shows the former extension of the pond or swamp 
near which it is met with. Several specimens, examined by the wri- 
ter, contained nothing but carbonate of lime mixed with a little sand ; 
but some are said to contain phosphate of lime. The substance on 
exposure to the atmosphere becomes about as hard as ordinary chalk. 
Calcareous tufa is a deposit of carbonate of lime on moss, twigs 
stones, &c., and is of very common occurrence in many of our smaller 
streams. Good specimens of a solid structure, capable of receiving a 
fine polish, are produced by some of the springs which issue from cre- 
vices in the Niagara escarpment, as at places near Hamilton, Rock- 
wood, Falls of Noisy River, and other localities along the line of coun- 
try through which the escarpment runs. A large deposit occurs also 
on the Beaver River, in the townships of Euphrasia and Artemisia. 
See under the ‘“‘ Niagara Formation,” above. 
Bog Iron Ore (see Parr II.) is a hydrated sesquioxide of iron, a 
variety of Brown Iron Ore or Limonite. It arises from the decompo- 
sition of iron pyrites and other ferruginous substances in rocks and 
soils, and the after solution of the oxide of iron, thus formed, by water. 
containing free carbonic acid or organic acids. The iron compounds 
dissolved by this agency, and carried into swamps and other low-lying 
places, are there deposited, and are subsequently converted into hy- 
drated sesquioxide. Patches of this kind are also occasionally found 
on hill tops and sides, by deposition from springs containing ferrugi- 
nous matter, This bog ore occurs in small quantities in numerous lo- 
