-28 The Interior of the Earth — Claypole. 
adhered to, represented even in the Devonian by two species, 
but that these two species really belong to Anodonta is by some 
•questioned. Dawson has described several allied forms from 
the Carboniferous of Nova Scotia; their family position however 
is as yet also unsettled. With these considerations in mind the 
bearing of the evidence thus far obtained is towards a high 
antiquity for this interesting group of bivalve mollusks, which 
now is so abundantly represented in all our ponds and streams. 
Crustaceans are represented, as is shown in the list, by two 
species; a Cythere^ and a trilobite of which only a single pygid- 
ium has thus far been found. Vetebrates are also rare — a 
few fin spines, about 2 cm. in length, and several dermal 
tubercles, and teeth. 
ON SOME INVESTIGATIONS REGARDING THE CONDITION 
OF THE INTERIOR OF THE EARTH. 
II 
BY PROF. E. W. CLAYPOLE, AKRON, O. 
Considering mathematically these evident inferences and 
treating tnem according to the law formulated by Prof. Darwin, 
Mr. Davison, of King Edward's School, Birmingham, England, 
has recently read before the Royal Society a paper in which he 
shows that in consequence of this law of contraction there must 
be a couche at some depth where the tangential compression 
•occurring at the surface and due to the rigidity of a crust in- 
capable of further contraction, must cease, and extension or as 
he calls it "stretching" must take its place. This result will as 
he shows occur whenever the horizontal contraction of a shell 
from cooling equals the diminution of space due to the total 
descent of all the shells below it from the same cause. A layer 
in that condition will descend as a whole and assume its new 
level without suffering either the lateral compression to which 
the couches above it are subject, (their contraction being less 
than their loss of room by descent,) or the extension to which 
those below it are subject, (their contraction exceeding their loss 
of room by falling into a sphere of shorter radius.) This shell 
