436 ON THE GEOLOGICAL RELATIONS 



have happened because the early earth, fluid from 

 heat in the interior, was less deeply covered by rocks 

 at its earlier periods, that much heat was extricated 

 during the act of consolidation, or during the pre- 

 cipitation of rocks from water, or during that of the 

 combination of their metallic bases with oxygen. Any 

 of these things are possible ; the general fact of a 

 lowering of temperature, were it but through radia- 

 tion, is probable : but of whatever other geological 

 value such a supposition or fact may be, it will not 

 bear on the present question, until the fact itself has 

 been established as to living and fossil beings ; which 

 it has not. But as this is an interesting subject, 

 which I cannot here discuss, I must refer, and chiefly 

 to Breislak and Fourrier. 



Of Colonies and of Transportations of organic 

 Fossils. 



These two circumstances respecting fossil remains, 

 interest geology far more than much that has pre- 

 ceded. The former proves conditions of repose, and 

 also periods of time ; being especially important to- 

 wards the proof of great duration in the intervals be- 

 tween successive revolutions. The latter is indis- 

 pensable to many inquiries respecting the changes of 

 the surface. 



If it is not universally true that particular tribes of 

 shells occur alone, it is a fact of sufficient frequency ; 

 as it is, that they lie undisturbed in the places where 

 they died. This happens notedly in the ammonites, 

 the cerithia, the nautilites, the nummulites, and others; 

 some of which also produce masses of rock of great 

 extent, even when of such microscopic minuteness 

 that a grain weight would counterpoise almost fifty. 

 The masses of rock thus formed entirelv of shells in 



