PAI^EOGEOGRAPHY. 275 



ported by an elephant, who, that he may not fall, is in his 

 turn supported by a gigantic tortoise; but the credulous 

 Brahmins are not permitted to ask on what the tortoise 

 rests. "We here venture on a somewhat similar problem, 

 though aware that we cannot hope to escape criticism. In 

 the astronomical portion of this work, reasons were given 

 which seemed to make it probable that our planet has 

 been formed from nebulous rings, separated from the solar 

 atmosphere, agglomerated into spheroids, and consolidated 

 by progressive condensation, beginning at the exterior and 

 proceeding towards the center. We will suppose a first 

 solid crust of the earth to have been thus formed, of which 

 the oldest silurian strata were the upper part. The eruptive 

 rocks, which broke through and upheaved these strata, rose 

 from depths inaccessible to our research ; they must have 

 existed, therefore, below the silurian strata, and were com- 

 posed of the same association of minerals which, when they 

 are brought to the surface, become known to us as granite, 

 augitic rock, and quartzose porphyry. Guided by analogy 

 we may assume that the substances which traverse the sedi- 

 mentary strata, and fill up their wide fissures, are only 

 ramifications of a great inferior mass. The foci of our pre- 

 sent volcanoes are situated at enormous depths; and, 

 judging from the fragments which, in various parts of the 

 globe, I have found imbedded in volcanic currents of lava, 

 I consider it as more than probable that a primitive 

 granitic rock is the substratum and support of the whole 

 edifice of superimposed fossiliferous strata. ( 334 ) Basalt, 

 containing olivine, does not shew itself before the cre- 

 taceous period, and trachyte still later ; but we find that 

 eruptions of granite certainly belong to the epoch of the 



