Then there would be four layers to the earth like the butternut

of the figure
Then there would be four layers to the earth like the butternut
of the figure. First, the inner kernel of gas; second, the hard
shell or endocarp; third, a viscous layer like the sarcocarp or
pulp, and outside of all the wrinkled crust of exocarp. If such
is the structure of the earth we may have in the very structure
of the earth itself a reason why from time to time there are
collapses of the middle layer leading to elevations of portions
of the outer rind, and marking off the chapters in geological
history, the lines between geological systems.