oe ae a ig eae 
Origin of the Continents of the Earth. 353 
ably infer, that over this naked portion, the surface first became 
solid, and has therefore cooled the longest and to the greatest 
depth.~ Consequently, the contraction from cooling, which was: 
going on, would take place most rapidly over the thinner and 
more yielding volcanic portion; and unless the ejections made 
up the difference, this part would become somewhat depressed, 
A melted globe of lead or iron in the same manner, when cooling 
unequally, becomes depressed by contraction on the side which 
cools last. Now on our own globe, the continents have to’a ve- 
Ty great extent been long free from voleanic action. A glance at 
amap of Asia and America will make this apparent. It is usual 
to attribute this almost total absence of volcanoes from the inte- 
nor of the continents to the absence of the sea; but it is fatal to 
this popular hypothesis, that the same freedom from volcanoes ex- 
isted in the Silurian period, when these very continents were’ 
mostly under salt water, a fact to which the wide spread Silurian 
tocks of America and Russia testify. Over the oceans, on the 
contrary, all the islands excepting the coral, are igneous—and the 
coral may rest as we have reason to believe on an igneous base. 
It is therefore a just conclusion that the areas of the surface 
constituting the continents were first free from eruptive fires. 
“portions cooled first, and consequently the contraction in 
progress affected most the other parts. ‘The great depressions oc-  - 
cupied by the oceans thus began; and for a long period after- 
ward, continued deepening by slow; though it may have been 
unequal, progress. This may be deemed a mere hypothesis ; if 
80, it is not as Jless as the common assumption that the oceans 
may have once been dry land, a view often the basis of geologi- 
reasoning. — 
_ Let us look farther at the facts. Before the depression of the 
Oceanic part of our globe had made much progress, the depth 
Would be too shallow to contain: the seas, and consequently 
whole land would be under water. Is it not a fact that in the 
‘Maly: Silurian epoch nearly every part of the globe was beneath 
l@ ocean? So we are taught by the extent of the formations. 
The depth of water over the continental portions would be very 
Vatious ; but those parts which now abound in the relics of ma- 
tine’ life, were probably comparatively shallow, as amount of pres- 
Sure, light, and dissolved air, are the principal circumstances 1n- 
Uencing’ the distribution of animals in depth, and acted former- 
Srconp Srrixs, Vol. II, No. 6.—Nov., 1846. . 
