. GEOGNOSTIC PERIODS. 285 



tion with which we are acquainted are slate and gra^wacke, 

 which contain some remains of sea weeds from the silurian or 

 Cambrian sea. On what did these so-called 7?iost ancie?U for- 

 mations rest, if gneiss and mica schist must be regarded as 

 changed sedimentary strata? Dare we hazard a conjecture 

 on that which can not be an object of actual geognostic observ- 

 ation ? According to an ancient Indian myth, the earth is 

 borne up by an elephant, who in his turn is supported by a 

 gigantic tortoise, in order that he may not fall ; but it is not 

 permitted to the credulous Brahmins to inquire on what the 

 tortoise rests. We venture here upon a somewhat similar 

 problem, and are prepared to meet with opposition in our en- 

 deavors to arrive at its solution. In the first formation of the 

 planets, as we stated in the astronomical portion of this work, 

 it is probable that nebulous rings revolving round the sun were 

 agglomerated into spheroids, and consolidated by a gradual 

 condensation proceeding from the exterior toward the center. 

 What we term the ancient silurian strata are thus only the 

 upper portions of the sohd crust of the earth. The erupted 

 rocks which have broken through and upheaved these strata 

 have been elevated from depths that are wholly inaccessible 

 to our research ; they must, therefore, have existed under the 

 silurian strata, and been composed of the same association of 

 minerals which we term granite, augite, and quartzose por- 

 phyry, when they are made known to us by eruption through 

 the surface. Basing our inquiries on analogy, we may assume 

 that the substances which fill up deep fissures and traverse the 

 sedimentary strata are merely the ramifications of a lower de- 

 posit. The foci of active volcanoes are situated at enormous 

 depths, and, judging from the remarkable fragments which I 

 have found in various parts of the earth incrusted in lava cur- 

 rents, I should deem it more than probable that a primordial 

 granite rock forms the substratum of the whole stratified edi- 

 fice of fossil remains.* Basalt containing olivine first shows 

 itself in the period of the chalk, trachyte still later, while erup- 

 tions of granite belong, as we learn from the products of their 

 metamorphic action, to the epoch of the oldest sedimentary 

 strata of the transition formation. Where knowledge can not 

 be attained from immediate perceptive evidence, we may be 

 allowed from induction, no less than from a careful comparison 

 of facts, to hazard a conjecture by which granite would be re- 



* See Elie de Beaumont, Descr. G^ol. de la France, t. i., p. 6.5 ; Beu 

 dant, Giologie, 1844, p. 1(\d. 



