HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 123 



to three great stages of diastrophism, a first, in which accessions to the exterior, 

 resulting in compression and heat, were dominant; a second, in which the transfer 

 of molten material from the interior to the exterior, involving the transfer of 

 heat, became dominant, this being the great volcanic stage that followed the 

 main stage of growth; and a third, embracing the hydro -atmospheric eon, includ- 

 ing most of the known geological history down to the present, in which dias- 

 trophism seems to have been dependent mainly on the re-distribution and loss of 

 heat and the internal re -aggregation of material, and subordinately on the shifting 

 of sediments. Obviously, these several stages were not separated by hard and 

 fast lines, but rather graded into one another insensibly, and constituted merely 

 successive phases of dominance. 



The Modes of Deformation. 



Reasons have already been given for believing that the water-covered areas 

 would acquire higher specific gravity than the land areas, and would, therefore, 

 take precedence in sinking, both in time and amount, and that thus the great 

 basins and the continental elevations would arise. If deformations were limited 

 to these greatest features of the earth's relief, the explanation might rest here; 

 but their surfaces are still further diversified by plateaus, anti-plateaus, and folded 

 mountains, as well as by the minor phenomena of faulted blocks, warped surfaces, 

 etc. Some of these, as the folded mountains, especially when attended by over- 

 thrust faults, imply a compressive lateral movement (Vol. I, pp. 500-510) ; others, 

 as the sunken blocks attended by normal faulting and gaping fissures, imply 

 crustal tension (Vol. I, pp. 510-525). The problem therefore embraces not only 

 the massive shrinkage supposed to have given rise to the abysmal basins and 

 continental platforms, but such accessory actions as were competent to give 

 rise to the plateaus, folded mountains, and lesser protuberances of a compressive 

 type, and to inequalities of a relaxative type. (For preliminary discussion see Vol. 

 I, pp. 542-589.) 



The earth may be conceived to be formed of great sectors whose bases are 

 the several ocean bottoms and continental platforms respectively, each con- 

 stituting a cone, py amid, or wedge, with its base at the surface and its apex at 

 the center of the earth. Assuming these factors, for the moment, to be units of 

 action, certain conceptions can be tested. 



1. If the sub-oceanic and continental sectors all shrank in equable propor- 

 tions in every part and simultaneously, the sectors would settle down within 

 their own spaces and no unequal crowding would follow, and hence no crumpling. 

 This is certaimy not the actual case. 



2. If the outer parts of all the sectors shrank proportionately more than the 

 inner parts, each sector could not only have settled down within its own space, 

 but could have permitted some tensional Assuring and faulting without involving 

 lateral thrust or folding. This is certainty not the actual case. 



3. If tha sub-oceanic sectors simply contracted radially more than the con- 

 tinental sectors, to the extent of about 3 miles, the continental-oceanic reliefs 



