382 Claypole on the Interior of the Earth. 
porphyries have a mineralogical composition which is ahnost 
identical with that of the granites. 8". The occuiTence of the 
rare manganese epidote, piedmontite, was noticed in three differ- 
ent specimens, and probably it has a much wider range. 9^ 
The structure of the porphyries varies from what was originally 
a vitropyre with the flow structure well developed, through the 
different grades of microfelsyte, granophyre, and micro- granite 
into the fine-grained granites. lo'^* The poryhyries have a 
structure, not described by others, for which the name pcecilitic 
is suggested. 1 1". The dykes seem to be of Archaean age, but 
possibly a few of them are younger. Nearly all of them trend 
from northeast to southwest, or approximately parallel to the 
Ozark hills. 13". Four general kinds of dyke rocks occur, the 
quartz-diabase, the uralite-diabase, the olivine-diabase, and the 
diabase-porjDhyryte. 13". The quartz-diabase is interesting on 
account of what seems to be primary, porphyritic quartz in so 
basic a rock. 14". The olivine-diabase is a very beautiful rock 
which is unusually well preserved. 15". The amount of glass 
in the big dyke at the "Tin Mines" decreases as we descend 
from the surface, so that specimens taken from the lowest 
tunnel show none. 
ON SOME INVESTIGATIONS REGARDING THE CONDITION 
OF THE INTERIOR OF THE EARTH. 
PROF. E. W. CLAYPOLE, AKRON, O. 
The condition of the interior of the earth is perhaps the 
most difficult problem with which geologists are now grappling. 
Progress is slow, necessarily slow. All work must from the 
nature of the case be done at arm's length or more so to speak. 
Inaccessible as are the depths of the sea we can reach them by 
the use of an immensely elongated slender finger — the sound- 
ing-wire with its grapnel and dredge. These implements ac- 
tually bring within our grasp some small specimens of .the 
material of which the bottom consists so that we ai'e able to 
handle and examine it in the laboratory. 
But we are totally luiable thus to reach and explore the in- 
