PRELIMINARY REMARKS, 
37 
element which is competent to explain many phenomena con¬ 
nected with changes of the earth’s crust. 
Rocks are fused in the interior of the earth’s crust, and in 
that state may rise to the surface. The fused rock often over¬ 
flows the brim of craters, and flowing down the mountain sides, 
breaks and vitrifies the rocks over which it flows, and fills the 
hollows in its line of march. So, also, fused matter may rise 
in the fissure formed by disruption, and after reaching the sur¬ 
face flow like a lava current over its edge, or force itself 
between the layers of a sedimentary rock. 
Internal heat must be regarded as an arrangement which 
conduces to the well being of the earth’s inhabitants. It no 
doubt ameliorates the cold, and sustains that degree of tempera¬ 
ture wdiich is best fitted to the organic and structural conditions 
of living beings. 
§ 32. Time is an element in geological dynamics . It is 
measured by forces whose operations we may witness. In the 
estimation of time we follow two methods, the results of which 
agree. The first method, we estimate the rate at which deposits 
accumulate in the present seas. The measuring line which we 
thus obtain is applied to the past. The second method is the 
reverse of the first. We estimate the amount of matter in the 
sedimentary rocks of all periods. This matter is composed of the 
wrnste of former continents and former mountain ranges. The 
sediments of each period are immense; and immense as our pre¬ 
sent mountain systems may be, still the sediments and wastes 
which have accumulated since animals and plants have lived, are 
sufficient to compose many such mountain systems as now exist. 
Life materially aids us in making our computations. It deter¬ 
mines the slow rate of the accumulations of which we have spo¬ 
ken. We are not to presume that the Prime Mover, the great 
Efficient Cause, has hastened events because he has the power. 
Events are preceded by preparatory steps, and time ancf events 
develop themselves in stages and periods. Like the planets in 
their orbits, they may be accelerated in motion for a moment, and 
