the Interior of tJie Earth. 279 



6. The crust of the earth, not including the superficial and 

 incomplete pellicle, which is named secondary, being formed 

 by refrigeration, it follows that consolidation has taken place 

 from without inwards, and consequently that the layers of the 

 original rocks nearest the surface are the oldest. In other terms, 

 the primordial formations are so much the more recent, the 

 deeper the level at which they occur, which is just the reverse of 

 what has hitherto been admitted in geology. 



7. M. Fourier, on considering the distribution of subterranean 

 heat at the depths which are accessible, the temperature of the 

 poles, and the existence of radiation toward the celestial spaces, 

 has demonstrated that the earth continues to cool *. This cool- 

 ing is insensible at the surface only, because the loss of heat there 

 is continually compensated by the effect of a propagation, which 

 uniformly proceeds from without inwards, a compensation which 

 is nearly perfect, which continually approaches the state of equi- 

 librium, and which experiment and theory perfectly explain. 

 The loss of heat has therefore no influence but at great depths, 

 whence there results, that the crust of the globe daily continues 

 to increase internally by new solid layers. Thus, the formation, 

 of the primordial strata has not yet ceased ; nor will it cease- 

 until after an immense period of time, that is to say, when the 

 cooling shall have attained its limit. 



8. If the crust of the earth has been formed in the manner 

 in which we suppose ii, the primordial strata with which we 

 are.acquainted ought to be disposed nearly in the order of their 

 fusibility ; I say nearly, for some influence must be attributed to 

 the rapid action with which the cooling must have been carried 

 on at the commencement of things, and that of chemical affini- 

 ties operating upon such large masses. Now, the magnesian, 

 calcareous and quartzose strata, are in fact the nearest to the sur- 

 face. 



9. According to what has been stated above, the mean thick- 

 ness of the crust of the earth probably does not exceed twenty 

 leagues of 5000 metres each. I would even say, that, according to 



• General Remarks on the Temperatures of the Globe and Planetary Spa- 

 ces, by M. Foiyier ; Annales de Chimie et de Physique, t. xxvii. 1824, 

 p. 136.; and Resumi theorique des Proprietes de la Chaleur rayonnante, by 

 the same, same volume, p. 275. ;«:-' y . i .Ci 



T 2 



