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POPULAR SCIENCE REVIEW. 
of Iuclia and China, the banks of the Mississippi, and the vast 
plains of South America, specimens of sculptured stone are 
obtained always precisely similar — that the jade of the East is 
mixed up in the caverns and gravel with flints from Western 
Europe, and with greenstones from America, and that even the 
northern parts of Australia and Madagascar appear to contain 
examples of manufacture differing from these nothing in style 
and little in material — we are reminded pointedly of the original 
unity of the human race, and we see that an undetermined 
cpiestion of time forms the only serious difficulty interfering 
with the reception of one of the most startling innovations 
resulting from modern geological investigation. 
Caverns, then, teach many truths in geology. First of all, 
they point, in their very form and in the mere fact of their exist- 
ence, to the grand operations of nature carried on out of our 
sight in the deepest recesses of the earth, — the conversion of 
mere heaps of mud and sand into definite stratified rocks, hard, 
durable, and characteristic. Next, they teach us how, when the 
rocks have been elevated, water lias acted upon them not only 
externally, but widening the narrow channels, removing and 
clearing out large spaces, and again filling them up with dif- 
ferent material. Thirdly, they show the nature of the inha- 
bitants of a former state of the earth’s surface, when climate 
and other physical causes determined the presence of races 
that have long since departed. Fourthly, they lay bare, some- 
times in the most singular manner, the secrets of marine life, 
and invite to a study of nature under circumstances of peculiar 
variety and interest. Fifthly, and lastly, they tell us a part of 
the great story of human existence, and of the association of 
man with many extinct races of gigantic quadrupeds, known 
only by their skeletons, but certainly characteristic of a 
geological period. 
