the Interior of the Earth, 281 



the phenomena of earthquakes, the thinness of the consolidated 

 crust, and especially the innumerable solutions of continuity, 

 by which it is broken up, and which result from stratification, 

 the contraction arising from progressive cooling, or from the 

 overturnings that have taken place, we long ago conceived it 

 probable that this crust possesses a certain flexibility. We de- 

 veloped the elements of this singular property in a memoir 

 read to the academy in 1816, and which had the disadvantage 

 of being presented at a period when people*'s minds were not 

 sufficiently prepared for attending to researches of this nature. 

 Now, this property is at the present moment more probable than 

 ever. It is further conceived, from the fluidity which is to be at- 

 tributed to the central matters that serve as a support to the 

 crust, that the flexibility in question may be j)ut into action with- 

 out its being possible for us to perceive it. In fact, to produce 

 a change of figure in the spheroid capable of raising the equator 

 a metre, by proportionally shortening the earth's axis, it would be 

 sufficient, in as far as concerns the plane of the equator, that 

 each of the innumerable solutions of continuity which intersect 

 the consolidated crust, and which I shall suppose to be five me- 

 tres from each other at an average, should be subjected to a se- 

 paration equal to the 1276th part of a millimetre, a quantity 

 which is excessively small. 



1 4. The probable flexibility of the earth's crust is supported by 

 two principal causes, the one general and constant, the other local 

 and transitory. The latter cause, during the last thirty years, has 

 not spared any country. Sometimes it has shaken, almost at the 

 same time, the twentieth part of the surface of our continents, or it 

 has made the soil undulate in directions equal to the sixtieth or 

 seventieth portion of a meridian ; I speak of eartliquakes. Since 

 the commencement of authentic history, there have been rec- 

 koned upwards of six hundred, whose violence or extent have 

 rendered them memorable. The second cause depends upon 

 the circumstance, that the permanent diminution of the earth's 

 heat no longer produces any sensible contraction in the subterra- 

 nean regions in the vicinity of the surface, while it continues its 

 effects in the deeper parts, whether for augmenting the separa- 

 tion of the masses which have experienced the first effects of 



