592 
They were generally almond-shaped and 
had a point or cutting edge at the small 
end; some of them made from ledge-rock 
and not from boulders, were brought to an 
edge all round. In outline they resemble 
the leaf-shaped implements of later ages ; 
but when viewed edge-wise the difference 
was manifest in that these were much 
thicker. The thickness is usually about 
half their width ; an implement four inches 
wide would be about two inches thick, and 
one two inches wide, an inch thick, while 
leaf-shaped implements of that width would 
not be one-half as thick. 
River Drifts, Valleys and Terraces. 
A further explanation is as to the forma- 
tion of the geologic deposits in which the 
implements were found, and so a decision 
as to their geologicage. It is believed that 
at an earlier period in the geology of the 
country the water of the rivers on its way 
to the sea eroded the earth (as is shown by 
the geologic models, principally of the 
Rocky Mountains, in the U. 8. National 
Museum) and formed valleys, making them 
reach from one hill to the other and as 
deep as the present bottom of the rivers ; at 
the second stage the water in the rivers, 
becoming less in volume and slower in 
movement, began the process which has 
been carried on from that day to the present 
in all river valleys, the cutting or washing 
of the river bank at or from one point or 
locality where the water ran swifter and 
stronger, and carrying it further down the 
stream where the water ran slower and 
weaker. In this manner the river terraces 
were formed, each successive terrace, 
counting from the hill, represented a cor- 
responding abasement of the water, until, 
as at present in many of our American 
rivers, especially the Ohio, three terraces 
exist on either side of the stream. In the 
chronologic formation of these terraces, that 
nearest the hill was the oldest, that nearest 
SCIENCE. 
[N. S. Vou. X. No. 252. 
the stream the latest. The bottom of each 
terrace was, naturally, laid down first and, 
consequently, was older than the top. So 
the bottom of the first terrace (nearest the 
hill) was the oldest, and the top of the ter- 
race (that nearest the stream) was the 
latest. 
These paleolithic implements have been 
found in the bottom of the first terrace and, 
consequently, were a part of the earliest 
deposit. And as they continued through- 
out the various terraces and in the different 
parts thereof, it is believed that the Paleo- 
lithic period in these localities began with 
the formation of the river-valleysand is co- 
existent with them. 
During all this period no implements of 
less enduring materia] than flint have been 
found, if any ever existed. No human 
remains have ever been found in the river 
valleys; nor the remains of any animal so 
small as man or whose bones were so light 
and frail as are his. 
Differences in Climate. 
No traces have been brought to light of 
either the habitation or the raiment of the 
man of this period. It has been suggested 
that he had no need for either. The cli- 
mate was warm, moist and rainy; he re- 
quired neither dwelling nor raiment to 
keep him warm or dry, for, like the savages 
of warm climates generally he may have 
preferred to run naked. This is regarded 
as entirely feasible in the climate then pre- 
vailing in western Europe. 
But there came a change, supposed to be 
represented by the glacial epoch, when the 
climate became cold and wet, and man re- 
quired protection and so was driven to the 
caverns for shelter. Here is found the 
first evidence of raiment. Thus began 
what has been called the cavern period. 
Epochs of the Cavern Period. 
Different classifications have been made 
and different names given to these. Some 
