212 FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
manent streams or bodies or fresh water. Furthermore, the sea¬ 
sonal distribution of the rainfall should be such as to pretty well 
balance the evaporation, otherwise the lakes and streams would 
fluctuate too much. 
GENERAL DISTRIBUTION OF PEAT 
Peat is most abundant in regions of immature topography, i. e., 
where processes of erosion and sedimentation have been at work 
a comparatively short time, for it is in such regions that bodies 
of still, clear water are most numerous. Lakes, ponds, swamps, 
bogs, etc., in whatever manner they may originate, are comparative¬ 
ly short-lived, geologically speaking, for they are almost sure sooner 
or later to be either filled with sediment washed down from ad¬ 
jacent slopes, or drained by the gradual deepening of the channels 
leading out of them, or both. Regions of mature topography 
have no lakes or ponds, and the valleys are typically steep and nar¬ 
row, with swift streams in them, toward their heads, and broad 
and level lower down. The lower courses of the streams are usu¬ 
ally sluggish enough, but they are apt to fluctuate too much or 
carry too much mud for the formation of peat 
In the eastern United States there are two extensive regions 
characterized by immature topography, namely, the glaciated region 
and the coastal plain. The glaciated region, which lies mostly 
north of the latitude of New York City, is believed to have been cov¬ 
ered many thousand years ago with a slowly moving ice-sheet, or 
aggregation of glaciers, which scooped out innumerable irregular 
depressions (determined largely by the location and character of 
the rocks and ridges) in the surface, deposited dams of rock and 
gravel across many of the valleys, and changed the face of the 
earth in other ways. After the ice retreated northward and the 
climate became warmer again these depressions quickly filled with 
water, forming the beautiful lakes for which some of the northern 
states are noted. The time elapsed since the glacial period—only 
an insignificant fraction of geological time—has been too short 
for stream erosion to have much effect on this region, especially 
as the soil left by the ice-sheet is very largely sand and gravel, 
which resists erosion pretty well.* Many of the smaller lakes 
of this region have long since become filled with excellent 
peat, and the process is' still going on actively in others. Similar 
conditions are found in Europe, mostly north of latitude 45 0 , and 
to a lesser extent in some other parts of the world. 
*In this connection see H. F. Cleland, Science II. 32: 82-83. July 15, 1910. 
