THOMAS. ] DR. LAPHAM’S CONCLUSIONS. Zo 
prostration. These “ wind-falls” are of frequent occurrence in the depths of the for- 
ests and occasion much difficulty in making the public surveys. The straight lines 
of the sections frequently encounter them. 
The amount of earth adhering to the roots of a tree when prostrated by the wind 
is, under favorable circumstances, very considerable, and upon their decay forms an 
oblong mound of greater or less magnitude, and a slight depression is left where the 
tree stood. These little hillocks are often by the inexperienced mistaken for Indian 
graves. From the paucity of these little ‘‘tree-mounds” we infer that no very great 
antiquity can be assigned to the dense forests of Wisconsin ; for, during a long period 
of time, with no material change of climate, we would expect to find great numbers of 
these little monuments of ancient storms scattered everywhere over the ground. 
Whether the greater extent of treeless country in former times was owing to nat- 
ural or artificial causes it is now difficult to determine, but the great extent of an- 
cient works within the depths of the present forests would seem to indicate that the 
country was at least kept free from trees by the agency of man. 
Many of these tree-mounds were observed on and about the ancient works. 
Another curious circumstance that may be noticed by inspection of the figures of 
mounds accompanying this work is the gradual transition, as it were, or change of 
one form into another, Examples can be found of all forms, from a true circle through 
the oval and elongated oval to the oblong mounds and long ridges. Again, there is 
a succession of mounds, from the simple ridge of considerable size at ene end and 
gradually diminishing to a point at the other, through the intermediate forms, having 
one, two, three, or four projections to the ‘‘turtle-form.” In this way, also, we may 
trace a gradual development (so to speak) of nearly all the more complicated forms. 
It is not pretended to assert that this was the order in which the mounds were 
erected; or that the aborigines gradually acquired the art by successive essays or les- 
sons. Indeed, we are led to believe that the more complicated forms are the most 
ancient. 
The relative ages of the different works in Wisconsin, so far as they can be ascer- 
tained from the facts now before us, are probably about as follows: 
First and oldest. The animal forms, and the great works at Aztalan. 
Second. The conical mounds built for sepulchral purposes, which come dewn to a 
very recent period. 
Third. The indications of garden-beds planted in regular geometrical figures or 
straight lines. 
Fourth. The plantations of the present tribes, who plant without system or regu- 
larity. 
Thus the taste for regular forms and ar-angements, and the habits of construction 
with earthy materials seems to have been gradually lost, until all traces of them dis- 
appear in our modern degenerate red men. 
The animal-shaped mounds and accompanying oblongs and ridges, constituting 
the first of the above series, are composed of whitish clay or of the subsoil of the 
country. 
The mounds of the second series, or burial mounds, are usually composed of black 
mould or loam, promiscuously intermixed with the lighter-colored subsoil. 
