58 BOTANICAL GAZETTE [AUGUST 
development and the succession of peat materials have to do with 
the factor of water content in the original area. Usually the 
quantity of water is more frequently concerned than its salinity, 
acidity, or alkalinity. The initial water relation, by its selective 
action, determines not only the characters of the life forms which 
establish themselves as the pioneer population, but also the number 
of layers possible and the order of their sequence. 
In a preceding paper (7) it was proposed to classify peat deposits 
of whatever nature into two great primary groups, the group of 
water-laid peat deposits and the group of land-laid peat deposits, 
in accordance as they have arisen in water or on partly drained 
but relatively moist initial areas. In the water-laid peat deposits 
the bottom layers consist of materials which accumulate only in 
standing water. They contain the remains of planktonic organisms 
and macerated material from plants more or less submerged or 
floating, or which occupied the margins of the basin. Subdivisions 
- of this group are given in the section which follows. In the land- 
laid group of peat deposits the origin is indicated in the mineral 
substratum by the vertical roots of plants which at one time 
occupied the area, as a well defined plant population or vegetation 
unit. The general stratigraphic subdivisions in this group are 
indicated by the order in which the vegetation units invaded and 
occupied the land area. With respect to the layers of peat material 
formed by them the order may be (1) progressive, that is, beginning 
with some member of the marsh group of peat materials until the — 
deciduous or coniferous forest climax of the region is reached; 
(2) stabilized, that is, it may begin and continue in a stable forest 
climax; or (3) the order may indicate the conversion of the basal 
forest climax into marsh and finally to open water conditions by 
the influence of various environmental causes. This distinction 
between the two primary groups of peat deposits is clear cut, and 
is readily made in field work. The only possible difficulty arises 
when the plant remains have been redeposited or partially removed 
by any later action, such as erosion. Even secondary disturbances 
of this nature, however, do not invalidate the importance of the 
stratigraphic viewpoint. Its significance for correlation studies 
has been sufficiently dwelt upon elsewhere (6). 
