1899 | DUNE FLORAS OF LAKE MICHIGAN 113 
hydrophytic beaches, partly perhaps because hydrophytic 
beaches are seldom sandy, and partly because they are com- 
monly found in protected locations. The hydrophytic beaches 
are found where the gradient of the lake bottom is very slight; 
as a consequence there is a wide zone of very shallow water in 
which typical swamp and shallow water plants flourish in great 
abundance. The bottom is very thickly strewn with gravel and 
shingle, closely resembling a reef in structure. On the other 
hand, a xerophytic beach is often sandy, is commonly associ- 
ated with steep clay bluffs or dunes, and the gradient is much 
steeper, so that there is a comparatively narrow zone of shallow 
water. As a consequence, wave action is much more pro- 
nounced on the beach proper, as is shown by the great amount 
of driftwood stranded there. The scanty flora is in striking 
contrast to the diversified flora of the hydrophytic beach. The 
Breater luxuriance of the flora on the hydrophytic beach is due, 
im part at least, to the greater freedom from the destructive 
action of the waves on account of the low gradient. The water 
Supply is also conspicuously greater on the hydrophytic beach, 
again chiefly because of the low gradient. Inasmuch as dunes 
are associated only with the xerophytic beach, no further refer- 
ence will be made to the other beach type. 
The xerophytic beach is essentially a product of wave action 
and comprises the zone which is or has been worked over by 
the waves. Hence the beach may be defined as the zone 
between the water level and the topographic form produced by 
other agents; in the region under study the upper limit of the 
beach is commonly a fringe of sand dunes or a bluff of clay or 
8tavel. The xerophytic beach in its typical expression is very 
naturally subdivided into three zones, which may be called the 
het cetin middle beach, and upper beach. The lower beach 
: Zone which is situated between the water level and the 
line reac 
middle 
by the highest winter storms. The upper beach is 
“ssentially a former middle beach which is now beyond the 
