533 Scientific Geology. 



perhaps, though not of the most violent kind, during the deposition of 



this formation. 



Theory concerning the Force by which Systems of Strata were elevated 



at successive epochs. 



Although existing volcanoes often occur at intervals along extensive 

 ridges of mountains, yet there is no evidence that such ridges have 

 been elevated by these volcanoes. Indeed, it is difficult to conceive 

 how a volcannic force can operate except in the direction of the radii 

 of a circle: so that however numerous the foci, they could not have 

 produced mountain ridges having a common direction through several 

 degrees of the earth's surface. Volcanic power then, in the common 

 acceptation of the term, could not have produced the systems of eleva- 

 tion that have been examined. 



If the theory of internal heat be admitted, however, we are furnished 

 with a power adequate to the production of these systems, as ingenious- 

 ly suggested by Beaumont. The outer crust of the earth, according 

 to the doctrines of central heat, has nearly reached the limit of refrigera- 

 tion : at least, it must cool much slower now than the internal parts, if 

 they are intensely heated: and consequently, the internal parts must 

 shrink much more than the exterior. Hence the envelope must from 

 time to time become too large to embrace the internal diminished parts, 

 without a suffering degree of plication. That is, in some places the crust 

 will sink down, and in other places be thrown up into correspondent 

 ridges. Mere gravity, would produce this effect, unless the crust had 

 become extremely rigid. And a little reflection will satisfy any one, 

 that these ridges and vallies will correspond in direction with the semi- 

 circumference of the globe; that is, with a great circle upon it: And 

 such is the direction which Beaumont supposes every known system 

 of strata has taken. 



According to this hypothesis, we see how it is that mountains should 

 be elevated at different epochs. For they result from the effort which 

 the crust of the globe is caused to make, from time to time, to accommo- 

 date itself to the continually diminishing size of the internal nucleus. 

 Whenever a cavity is thus produced underneath any portion of the 

 crust, its weight will cause its thickest or least rigid portions to sink down 

 upon the heated and it may be fluid nucleus, and this will produce a 

 lateral pressure sufficientto elevate adjoining portions; while the weight 

 of the depressed portion will force the fluid matter into the cavities pro- 

 duced by the elevations; and it may be, even cause it to be erupted 

 through the ruptured summits of the ridges : thus producing unstrati- 



