1918] ROBBINS—BOULDER PARK 517 
ceratophylla (Hook.) Piper, Achillea lanulosa Nutt., Antennaria 
parvifolia Nutt., and Crepis perplexans Rydb. The large number 
of characteristic meadow species will be noted. 
The depth of the peat deposit in the lake was determined 
throughout. In the center it is over ro ft. deep. From here the 
depth gradually decreases toward the shores. The rate of increase 
in depth may be judged by a set of borings made every 5 m. along 
an east-west line to the center of the area. Starting at the east 
shore this series shows depth (in cm.) as follows: 40-46-47-43-70- 
136-180-212—220-258—over 300. 
Borings show that the lake has been filled almost entirely with 
the stems and leaves of Carex. The surface soil is loosely packed 
plant material, readily separated into layers, indicating seasonal 
deposition. The upper 6-8 inches are light brown in color; below 
this, the layers become darker and more compact. This soil 
exhibits a slight acid reaction. : 
It will be recalled that, at East Lake, Salix chlorophylla is a 
characteristic plant of the raised rim at the water’s edge. A similar 
condition exists here. At the west shore there is a very distinct 
line of this shrub, on a more or less evident rim; at one time these 
formed a fringe at the water’s edge. Back of this rim is a belt 
averaging about 20 ft. wide, clearly the old sedge moor of the lake 
shore. Beyond this is a meadow scrub, followed by herbaceous 
meadow, then dry grassland. The dry grassland is not the outcome 
of progressive drying of the meadow, as the zonation might sug- 
gest, but it represents a stage in a xerarch succession on the glacial 
gravel of the high terrace. 
DRY GRASSLAND SUCCESSION 
The rapid drainage of the lake which covered the entire park 
left a level, uniformly gravelly, area exposed to the drying and 
mechanical effects of the winds, and the extremes of diurnal and 
yearly temperatures. Lichens and Selaginella densa are the chief 
Pioneers of the glacial gravels here. The latter is a mat former, and 
on the mats other plants gain a foothold. Its reaction upon the 
habitat, in holding the soil, adding humus, and retaining water, 
favors the entrance of such xerophytes as Erigeron multifidus Rydb., 
