MOVEMENTS AND DEFORMATIONS 361 



2. The resisting agencies. The condensing agencies are more 

 or less held in check by resisting agencies. Heat is the most familiar 

 of these. It is abetted by molecular and atomic arrangements, and 

 by factors in the ultimate structure of matter, not as yet under- 

 stood. It has been usual to regard the primitive state of the earth 

 as one of intense heat, and to assign its subsequent reduction of 

 volume almost solely to loss of heat. This is not the view here 

 favored. On the contrary, the heat is supposed to have been 

 chiefly developed by forceful reduction of volume. The heat thus 

 developed is one of the forces which check the further decrease 

 of volume. Loss of heat is a cause of shrinkage, but its effect is 

 thought to be less than that of molecular, atomic, and sub-atomic 

 rearrangements of the material of the earth. 



The Original Distribution of Heat 



Very different views as to the original state of the matter of 

 the earth are entertained according as the older or the later hy- 

 potheses of the origin of the earth are followed. These will be set 

 forth in Chapter XII. 1 In the hypotheses which assign to the young 

 earth a molten state, the original temperature is usually held to 

 have been high, and its distribution somewhat uniform through- 

 out the interior. Cooling afterward affected only a moderate 

 depth, usually computed to be little more than 200 miles. Under 

 the planetesimal hypothesis, which is here favored, the theoretical 

 distribution of the internal heat arising from compression is shown 

 in Fig. 288. The nature of this distribution is such that heat would 

 be conducted from the deep interior to the outer zone 800 to 1,200 

 miles thick, faster than from the latter onward, with the result of 

 raising the temperature of the outer zone while that of the deep 

 interior falls. The result of this should be a severe crowding of the 

 outer zone upon itself, in shrinking to fit the deep interior as it 

 loses heat and shrinks. This crowding of the thick outer zone 

 upon itself is the assigned cause of the great deformations .that 

 gave rise to the abysmal basins and the continental platforms. 

 Very important discoveries have recently been made relative 



1 They may be found more fully stated in the authors' larger work, Vol. 

 I, pp. 559-574 and Vol. II, pp. 1-81. 



