412 
TU£ GEOLOGIST. 
"would go to form the lower strata of the globe, whilst the upper 
might owe their origin both to the subsequent erosion of the first 
strata deposited, and also to vast eruptions of volcanic matter from 
the interior of the yet unsettled earth. The admission of the latter, 
the volcanic agency, fully accounts for the great variety of mine- 
rals and metals found deposited in rocks during different ages, 
whilst the varying character of lavas ejected in the same localities, 
yet separated by long intervals of time, would in some measure show 
the reasonableness of the supposition that the interior of the globe 
is in reality the grand repository whence every mineral had its 
origin.* 
Assuming the nebular theory to be correct, the following would 
appear to be the sequence of changes occurring during the earth's for- 
mation. 
All matter existing originally in the form of a gaseous mass, the 
particles of which were kept separate by the contained caloric, on cool- 
ing to a certain point, the least easily volatizable parts would assume 
either a solid or a liquid form. Immediately on this taking place, the 
particles so forming, would of necessity rush together by the force of 
gravity, and must inevitably meet and form a solid or liquid nucleus to 
a surrounding nebulous atmosphere. The contained lieat of the nebu- 
lous atmosphere still further decreasing, other solid or fluid matter 
would be formed, and would be deposited in the form of a stratum 
upon the solid or liquid portion first originated. In this way would 
be built up, as it were, avast globe, whose materials would be arranged 
in layers or strata, the order or position of which would be the order 
in which they respectively solidified. f 
During the formation of such a globe, it might sometimes happen 
that a stratum of a greater specific gravity would immediately suc- 
ceed one of less. If the former chanced to remain a fluid, it is evi- 
dent the two would be placed in a state of instable equilibrium, and 
that the, at first, lower stratum would, by the inevitable laws of gra- 
vity and hydrostatics, ultimately assume the higher position. This 
state of things may be realized by imagining iron or other light metal 
and mercury to be introduced, both in a state of vapour, into the same 
receiver. If the lighter metal were the first to assume the solid 
form, it would be naturally deposited upon the bottom of the con- 
taining vessel, but would rise to and float upon the surface of the 
mercury immediately on the lattei-'s condensation. 
Applying this theory to the formation of the globe, let us suppose 
the granite at a given period to have been already precipitated, the 
heat of the nebulous mass being diminished by a required amount ; and 
upon this layer of granite to-be subsequently thrown down a fluid of 
* In New Zealand there is said to be miles and miles of fine steel-dust covering the 
scabeacli to a considerable depth ; this dust is supposed to be ejected by volcanic action. 
t So far, most part of the above theory is identical with that of M. Ampere, noticed 
in the ' Edinburgh Philosophical Journal,' vol. xviii. p. 339. The author, however, begs 
to state that he never heard of M. Ampere's theory until long after his own had been 
elaborated. 
