458 FRESH-WATER SHELL-HEAPS 
extent to which vegetable substances were made use of, the — 
shell-heaps offer no evidence ; but it seems certain, that until — 
_ the bow and arrow, the trap or the net were invented, the : 
animal food must have of necessity been derived from such — 
species as could most easily be obtained, and among these 
the shell-fish and the more sluggish reptiles would first at- 
tract attention. . 
Ill. AGE. 
No satisfactory data were found for determining the age 
of the shell-heaps. The appearance of great age which some 
of them have, as at Horse Landing and Old Enterprise, is 
important; the same may be said of the fact that the bones — 
embedded in them had lost nearly all their organic matter, 
and at both of these places were incrusted with calcareous — 
deposits, in some instances forming a conglomerate. The 
time required for these last results is not necessarily vey — 
great, but the organic matter of bone is destroyed vety 
slowly, and is largely present in those of some of the extinct 
animals. We have obtained a larger quantity of animal a 
matter from the bones of the Mastodon than from those 0 
the deer at Old Enterprise. 
The most trustworthy records are found in the forest trees 
growing upon the mounds. These give us a minimum age 3 
with some approach to accuracy. The live-oaks (er 
virens) are not only long-lived, attaining an age of many i 
centuries, but their wood is the most durable of all the forest . 
trees of the United States. One of these, which had : ar 
from the effects of age, lies upon the top of a mound in = 
woods near Blue Spring, and measures five feet and s 
inches in diameter. As it was on the summit of the mo" i 
it could not have begun to grow until the mound was pee 
or quite finished ; it may have begun many years me 
had been dead for a long time ; its bark, all of the s™® 
most of the large branches had disappeared. 
. after they are dead still remain erect for many yea! 


