918 _GEOGNOSY AND GEOLOGY. 
the sea, and confirmed by the occurrence of chlorine combinations, 
of nitrogenous substances and bitumen. The steam may be produced 
from the water existing in the abyss, and also by the re-combination of 
hydrogen and oxygen of the atmosphere. The oxydes thus produced are 
melted together in the hearth of the gigantic furnace by means of heat 
derived oon the central fires, as also from the oxydation itself, and in the 
form of lavas are vomited up over the blooming fields, carrying death and 
destruction in their path. 
V. THE SURFACE OF THE EARTH IN GENERAL. 
In considering the external form of the earth, and of the relations between 
normal and abnormal masses, we have seen brought in review before us moun- 
tains and valleys, land and water. The mountain is seen to be nothing else 
than a slight elevation above the general level, and the watery surface only a 
filling up of a depression. Yet, however fortuitous all these features may 
appear to be, an attentive observation reveals to us the existence of certain 
laws influencing the general result. 
‘The elevations in the form of mountain chains contribute very essentially 
to the character of our globe. These had certainly never arisen but for the 
longitudinal disturbance by plutonic masses of the original horizontal position 
of the rock strata. The position of the strata thus appears to be dependent 
upon plutonic masses, as may be observed in almost all mountain chains: the 
cases are indeed rare where this conclusion is unsupported by actual exhibition 
of these masses themselves. Even if certain changes are not attributable to 
such masses, they may belong to some of their concomitants, such as the vapors 
produced in the interior of the earth. Pl. 47, fig. T, presents a comparative 
view of the principal mountain heights of the old world; jig. 8 does the same 
for the new. 
Volcanoid and voleanic masses are of much less importance in influencing 
theaeneral shape of the earth; they only form domes, single mountains and 
hills, upon localities furnished to them by plutonic rocks. 
It is exceedingly difficult, if not absolutely impossible, to picture to our 
minds the condition of the earth at its first period of development. 
Speculative geology or geogeny may indeed endeavor to penetrate to the 
bottom of all the phenomena and facts which are furnisbed to it by geognosy 
as a purely empirical science: it may seek to develope the causes which 
have produced such mighty effects, and thus pass itself step by step to the 
primeval condition of our planet, to speculative hypotheses as to its original 
shape, to the laws according to which its fashioning proceeded, to the causes 
upon which depended the successive changes on its surface. And these 
speculations may not be disregarded, but their application must be made 
with all due caution, that the proper and legitimate bounds of reasoning be 
not overstepped. According to Laplace, the earth, with the entire solar 
system, at one time, was a vastly diffused nebulous mass, set in rotary 
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