26 COSMOS. 



throw some degree of light on the history of the atmosphere, 

 and the distribution of the organic bodies imbedded in the 

 solid crust of the earth. This study enables us to understand 

 how a tropical temperature, independent of latitude (that is, 

 of the distance from the poles), may have been produced by 

 deep fissures remaining open, and exhaling heat from the 

 interior of the globe, at a period when the earth's crust was 

 still furrowed and rent, and only in a state of semi-solidifi- 

 cation; and a primordial condition is thus revealed to us, 

 in which the temperature of the atmosphere, and climates 

 generally were owing rather to a liberation of caloric and of 

 different gaseous emanations, (that is to say, rather to the 

 energetic re-action of the interior on the exterior,) than to the 

 position of the earth with respect to the central body, the 

 sun. 



The cold regions of the earth contain, deposited in sedi- 

 mentary strata, the products of tropical climates ; thus, in 

 the coal formations, we find the trunks of palms standing 

 upright amid coniferae, tree ferns, goniatites and fishes 

 having rhomboidal osseous scales ; * in the Jura lime- 

 stone colossal skeletons of crocodiles, plesiosauri, planulites, 

 and stems of the cycadeae; in the chalk formations, small 

 polythalaniia and bryozoa, whose species still exist in our 

 seas ; in tripoli, or polishing slate, in the semi- opal and the 

 farina-like opal or mountain meal, agglomerations of siliceous 

 infusoria which have been brought to light by the powerful 

 microscope of Ehrenbergf ; and lastly, in transported soils, 



* See the classical work on the fishes of the old world by Agassiz 

 Rech. sur les Poissons Fossiles, 1834, vol. i. p. 38 ; vol. ii. pp. 3, 28, 34. 

 App. p. 6. The whole genus of Amblypterus, Ag. nearly allied to Pa- 

 Iseoniscus (called also Palaeothrissum) lies buried beneath the Jura forma- 

 tions in the old carboniferous strata. Scales which, in some fishes, as in 

 the family of Lepidoides (order of Ganoides), are formed like teeth, and 

 covered in certain parts with enamel, belong, after the Placoides, to the 

 oldest forms of fossil fishes ; their living representatives are still found in two 

 genera, the Bichir of the Nile and Senegal, and the Lepidosteus of Ohio. 



f [The polishing slate of Bilin is stated by M. Ehrenberg to form a 

 series of strata fourteen feet in thickness, entirely made up of the siliceous 

 shells of Gaillonella, of such extreme minuteness, that a cubic inch of 

 the stone contains forty-one thousand millions ! The Bergmehl (moun- 

 tain-meal or fossil farina), of San Fiora, in Tuscany, is one mass of 

 animalculites. See the interesting work of G. A. Mantell, On the Medal* 

 if Creation, vol. i. p. 223.] TV. 



