62 BOTANICAL GAZETTE [AUGUST 
a notable example. The coastal river and estuarine peat-lands 
merge into the (3) marine deposits such as tidal marsh and 
mangrove swamps. A discussion of the brackish and salt water 
deposits is reserved for a future paper. 3 
Ev IDENCE OF CLIMATIC CHANGES 
It might seem that the water-laid group of peat deposits could 
not offer reliable and direct criteria for evaluating age or time 
correlations, since water in basins constitutes a fairly uniform 
environment. There is continuity in the sequence of strata of 
plant remains, but macerated and more or less structureless layers 
of peat material bear no fixed relation to the plant populations 
which succeeded each other in the development of the deposit. 
The organic fragments are derived from many sources, and are 
in large part from suspended débris. Nevertheless, inferential 
evidence of past vegetation units and climatic changes may occur 
in abundance. . 
The evidence for age and for climatic correlations is of several 
kinds, of which one form is represented in the scattering and mixing 
of leaves, pollen, and seeds blown into a peat deposit or washed 
in from adjacent land vegetation units. The latest substantial 
comparison between plant remains (such as the pollen of conifers) 
in layers of peat material and the changes i in climate and in the 
composition of land-plant communities is the quantitative method 
employed by von Post (24). 
A second kind of evidence of climatic changes found in peat 
deposits consists of dark colored, partly macerated, and fibrous layers 
of material alternating with predominantly finely fibrous, coarsely 
fibrous, or woody plant remains. The close association of this 
kind of stratification in practically all sorts of peat deposits, without 
any close relation to topography or the influence of animal agencies, 
appears to signify alternating wet and dry environmental condi- 
tions. Quite frequently the dark colored, partly fibrous layer of 
peat material is referred to by American writers as “well decom- 
posed peat.’’ Although it bears a striking superficial resemblance 
to a finer texture, similar to weathered surface material, a layer of 
this character does not imply conditions of aeration, or of warmth 
