412 BROOKLYN BOTANIC GARDEN MEMOIRS 
factors. In various places the decomposed remains of an earlier 
vegetation led to mechanical and chemical changes in the soil, the 
extent of which was more effective toward breaking up the flora into a 
heterogeneous formation, accompanied by a frequent replacement of 
one dominating group by another.”’ 
There are some bogs without evidence of marl at the bottom. 
Davis reports all the many peat bogs examined by him in Maine as 
resting on sand, clay or rock bottom, none on marl. Most of the 
peat bogs in the Adirondack region of New York have no marl at the 
bottom. These presumably were from the first supplied by springs 
of non-alkaline water. Some of the peat bogs of central and western 
Fic. 2. Peat bog near McLean, Tompkins Co., N. Y. Chamaedaphne, Andro- 
meda, Ledum and other heaths together with Sphagnum form the dominant vegeta- 
tion. 
4 
New York have great masses of marl under them. Such a one is near 
Peterboro in Madison County and another on Gorham Creek in On- 
tario County. Here it is apparent that some agency changed the 
composition of the water to such an extent that oxylophytes found 
conditions congenial. 
The most extensive marl ponds in the region are in the vicinity 
of the limestone belt of central New York. They occur at West 
Junius in Seneca County and southwest of Rochester, especially at 
Bergen in Genessee County. Isolated and much smaller marl ponds 
