Shaler.] 238 



Cambridge, Mass.yin the autumn of 1865. Only a preliminary state- 

 ment is meant to be given of views wliich the author will hereafter 

 endeavor to establish, by adducing the j^henomena which have led to 

 their adoption. 



We are indebted to the simultaneous thought of Charles Babbage 

 and Sir J. Herschel for the following conclusions concerning the eifect 

 of movement of the isogeothermal lines, and the causes competent to 

 produce such movement. 



1st. That the isogeothermal lines, at least in those regions near the 

 surface, have their jDOsition determined by the thickness and conduct- 

 ing power of the materials constituting the solid crust ; and that any 

 considerable increment of non-conducting material at any point on 

 the surface, would result in changing the position of the isogeother- 

 mals, bringing the lines of equal heat nearer the original surface. 



2d. That by this means the lines representing the points of equal 

 heat must be constantly rising in those portions of the earth's crust 

 exterior to which deposition of strata is taking place, and that such 

 an accession of heat into previously unheated strata must produce a 

 great expansion of their mass ; and as a consequence, we may have a 

 considerable vertical uplift of the outer surface of the crust. These 

 theoretical speculations are adduced by Mr. Babbage to account for 

 observed phenomena of local elevation. 



Accepting these conclusions as to the effect exercised on the move- 

 ment of lines of heat by deposition, and the effect of such intruding 

 heat in expanding the ordinary materials composing strata, it is 

 at once evident that such expansion must act horizontally as well 

 as vertically, producing a tendency to lateral as well as perpendicular 

 movement. On consideration it will be manifest that the result of 

 this lateral expansion, from the great elevation of temperature of the 

 lower portion of the solid crust, would be a tendency of the whole area 

 over which deposition was going on, to cm've downwards. For the sake 

 of illustration, this tendency may be advantageously compared to the 

 movement resulting from the application of heat to a bar composed 

 of two strips of metals having different coefficients of expansion ; the 

 resulting flexure is always in the direction of the material having the 

 greatest rate of expansion. In the case of the earth's crust, the 

 same effect, produced in the metallic bar by different rates of ex- 

 pansion, is brought about by different amounts of heat received by 

 the upper and lower parts of the crust, from the change of posi- 

 tion of the isogeothermal lines. While the deposition of one mile 

 of vertical depth of strata at any given point on the earth's surface 

 would not affect the heat of the crust near the surface, to such 

 an extent as to produce any considera1)le expansion, the effect on 

 deeper portions would be very considerable. 



