Senry Woodward — Address to the Geologists' Association. 537 



equal conductivity along every radius, then the cooling and the con- 

 sequent contraction along each radius would he equal, and, so far as 

 this cause is concerned, the earth, though hecoming smaller, would 

 maintain its symmetry of form and its universal ocean. But such 

 homogeneity could not be expected, nor does it exist. In a hetero- 

 geneous earth thus cooling, areas of greater conductivity would cool 

 more rapidly, and therefore contract more raindly in a radial direc- 

 tion. These more conductive areas with shorter radii would form the 

 sea-bottoms, while the less conductive and therefore less radially 

 contracted portions would become land-surfaces. The accumulation 

 of water on the shorter or more contracted radii would not check the 

 process : for although water is a bad conductor, yet it conveys heat 

 from the bottom to the surface by convection with great rapidity : 

 and therefore the process of cooling through a stratum of water 

 would go on far more rapidly than through a stratum of any rocky 

 material. The same process continuing would tend constantly to 

 increase the inequalities thus commenced. In other words, the sea- 

 bottoms would sink, and the continents increase in size and height. 

 (Joseph Le Conte.) 



Thus, through the unequal contraction of the earth's crust, by 

 which the great continental areas were originally elevated as vast 

 anticlinals above the general ocean, the first preliminary stage 

 necessary for the commencement of mountain-formation would be 

 accomplished. 



From this date sedimentary deposits on the largest possible scale, 

 resulting from, meteoric action over the newly-made continents, would 

 begin to accumulate in the great submarine synclinals parallel to the 

 coasts. 



It is a well-known fact, first brought prominently forward by 

 Prof. James Hall, that mountain-chains are composed of enormous 

 masses of sediments 10,000, 20,000, or even 40,000 feet in thickness. 

 How have these vast masses — accumulated at such low levels — been 

 elevated, not merely on a line with the continent itself, but thousands 

 of feet above the sea ? And why does the yielding to horizontal 

 pressure take place along these lines of deposit in preference to any 

 other ? 



Prof, Joseph le Conte suggests that the answer is to be found in 

 the theory of the aqueo-igneous fusion of deeply-buried sediments. 



The accumulation of sediment, as first shown by Scrope, Babbage, 

 and afterwards by Sir John Herschel, necessarily produces a rise of 

 the geo-isotherms, and an invasion of the sediments by the interior 

 heat of the earth. From this cause alone, taking the increase of 

 interior heat at 1° for every 58 feet, or about 90° per mile, and adding 

 the mean surface temperature (60°), the lower portion of 10,000 feet 

 of sediments must be at a temperature of about 230°; and of sediments 

 40,000 feet thick, like those of the Appalachian chain, must be 

 nearly 800° Fahr. Even the former moderate temperature, long 

 continued in the presence of the included water of the sediments, 

 would be sufficient to produce incipient change — at least segregation, 

 if not metamorphism. In fact, segregation of sediments will pro- 



