1890. ] The Persistence of Plant and Animal Life. 521 
plant, from inorganic material; etc, etc., which do not concern 
the main question of the essential continuity of inorganic with 
organic force, and the separation of the phenomena of the latter 
from those of the former by an indefinable line. No hard and 
fast line can be drawn to separate animal from plant, and none to 
separate plant from crystal. The force which is the cause of 
production and of change seems as if it were simply modified to 
suit the various structures which it builds. The material in all 
three kingdoms of nature is without doubt the same. One force 
—one matter—is foreshadowed here. 
It will be advisable to look a little more closely at this material. 
The most generally accepted hypothesis of the evolution of the 
solid earth on which we live begins with La Place’s celebrated 
generalization of the condensation of tenuous material,—first to 
vapor ; then to liquid ; then to solid, at an intensely high temper- 
ature ; and finally by cooling to the globe-that we know. 
Dr. T. Sterry Hunt (Chem. and Geol. Essays) has taken up the 
history where La Place leaves it, or at the stage where the in 
great part molten earth is covered by a thin shell of rock, like 
lava or basalt, upon which descend acid rains containing 
hydrochloric, sulphuric, and nitric acids, hitherto kept in suspen- 
sion by the intensely high temperature. The crust on which 
these rains descend would necessarily be made of the lightest 
elements combined together ; the heaviest would be found near 
the centre of the earth. 
These lightest materials, which while in fusion floated on the 
rest like an ocean, would consist of silica and the alkalies and 
alkaline earths, with some of the rarer elements. On this subject 
a recently published memoir of Prof. F. W. Clarke, Chemist of 
the U. S. Geological Survey, is extremely interesting. Prof. 
Clarke has for the first time systematically investigated the com- 
position of the crust of the earth for a depth of ten miles from 
the surface, by comparing a great number of analyses of the var- 
ious rock strata of different parts of the world with each other.* 
3 Relative Abundance of Chemical Elements, by Frank Wigglesworth Clark , Philo 
sophical Society of Washington Bulletin, Vol. XI., pp. 131-142. 

