Mr J. D. Dana en the Volcanoes of the Moon. 31 



.except 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 sur- 

 face constituting the continents were fa*st free from eruptive 

 fires. These portions cooled first, and consequently the con- 

 traction in progress affected most the other parts. The 

 great depressions occupied by the oceans thus began ; and for 

 a long period afterward, continued deepening by slow, though 

 it may have been unequal, progress. This may be deemed a 

 mere hypothesis ; if so, it is not as groundless as the com- 

 mon assumption, that the oceans may have once been dry 

 land, — a view often the basis of geological 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 conse- 

 quently the whole land would be under water. Is it not a 

 fact that, in the early Silurian epoch, nearly every part of 

 the globe was beneath the ocean \ So we are taught by the 

 extent of the formation. The depth of water over the conti- 

 nental portions would be very various ; but those parts which 

 now abound in the relics of marine life, were probably com- 

 paratively shallow, as amount of pressure, light, and dissolved 

 air, are the principal circumstances influencing the distribu- 

 tion of animals in depth, and acted formerly, we may believe, 

 as at the present period. Here, then, we see reason for what 

 has been considered a most improbable supposition, the exist- 

 ence of an immense area covered in mast parts by shallow 

 seas, and so fitted for marine life. 



If we follow the progress of the land, we find that with 

 each great epoch there has been a retiring of the sea. In the 

 coal deposits we have an abundant land vegetation. Subse- 

 quently, the progress on the whole was giving increased ex- 

 tent and height to the land, and diminishing the area of the 

 waters. Instead, therefore, of a bodily lifting of the conti- 

 nents to produce the apparent elevation, it may actually have 

 been a retreating of the waters through the sinking of the 

 ocean's bottom. The process, however, has not been a con- 

 tinuous one ; for during each epoch — the Silurian and the 

 more recent — there have been subsidences as well as seem- 



