162 J. D. Dana—Results of the Earth's Contraction. 
neath which the solid nucleus of the globe reached nearest to 
the surface; for this approach to the surface would have been 
favored by the chemical quiet ; and the less depth would have 
insured more rapid cooling. 
The solid state of the interior mass, under the Hopkins’ 
theory, is due to the pressure of the outer portion, this pressure 
being capable of producing an increase of density, and, at some 
depth, that density which belongs to the solid rock ; so that 
downward, either from the plane at this depth, or from some 
level or levels below it, actual solidity would have existed. It 
may be that when exterior solidification, that is, the solidifica- 
tion of the crust, was about to begin, the outer limit of the 
interior solid mass over the solidifying areas was quite up to 
existing. 
3. Nature of the cooling crust, and of the liquid layer of which it 
was formed. 
pie clusions, appealed to effectually by Daubrée,* is the consti- 
ion 
arrive at the following conclusions. 
(a.) The more prominent minerals were the following. (1) 
Some iron-bearing species (bearing also magnesia and lime) of 
the amphibole family, as augite, hornblende; (2) the iron-and- 
magnesia mineral nad wees (or olivine), to which Daubrée, on the 
evidence just referred to, gives great prominence; (3) species of 
*Expériences synthétiques relatives aux Météorites. ochements au% 
quels elles conduisent, tant pour la formation de ces corps planctaires que pour ¢" 
du globe terrestre; par M. Daubrée. Comptes Rendus, Lxii, 1866. 
