239 [Shaler. 



The same reasoning which leads us to conclude that over sea bot- 

 toms where deposition is going on there is a tendency to subsideiice, 

 leads us to the opposite conclusion with regard to those portions of the 

 earth's crust which are above the water level, and over which degra- 

 dation is taking place. This removal of material which is going on every 

 where over the surface of the subacrial portions of the Crust, must 

 result in driving the isogeothermal lines toward the centre, in the 

 gradual cooling of beds previously heated, and in the addition to the 

 lower portions of the crust, of soHd material gained from the viscidly 

 fluid nucleus as the downward cooling progresses. These changes 

 would evidently result in giving to such regions of the crust a tend- 

 ency to bend upward, or in the reverse direction, from a similar move- 

 ment of the ocean floor. 



The process of accommodation of the hardened outer crust to the 

 nucleus diminishing from loss of heat, requires the formation of ridges 

 and valleys which will occur in such places, and of such size as the 

 condition of the crust determines. Let us suppose that during any 

 geological period the earth has parted with sufiicient heat to require 

 a readjustment of the crust to the reduced nucleus. At what point 

 wiU the upfold take place and where the downfold ? Manifestly at 

 those points where there exists some tension acting in those directions. 

 Such tension we have seen is given to the crust by the actions of deg- 

 radation and deposition, and it follows therefore that when readjust- 

 ment of the crust to the nucleus takes place, the resulting flexm-es 

 will be upward over the subaerial portion of the crust, and down- 

 ward over the subaqueous portion. This action will necessarily be 

 complicated by the operation of other causes than that mentioned ; 

 the transfer of weight from one portion to another of a comparatively 

 rigid crust, would necessarily tend to produce similar results on the 

 direction of flexure. The most prominent effect of this transfer of 

 weight would be a tendency to produce fractures extending through 

 the crust at points near the shore line. Such fractures would extend 

 through the superincumbent strata into beds which had been greatly 

 heated by the deposition of the mass which had produced the fracture, 

 and the result would be the formation of vents for the pent up gases 

 of the heated strata, along shore lines, presenting the series of phe- 

 nomena we have exhibited in volcanic fissures. 



Assuming the original nuclei of the continents, or the points first 

 elevated above the sea level, to have been in the northern portion of 

 the existing continents, a view which it would not be difficult to show 

 to be eminently probable, it is believed that continents wosild increase 

 southwardly in a succession of southward pointing triangles through 

 the action of the before mentioned causes. 



