44 



OUTLINES OF GEOLOGY. 



this analogy was not identity, and it is to the study of their 

 fossils, by Brogniart and Smith, that we are indebted, prin- 

 cipally, for becoming acquainted with their true nature. 



93. The formations of the superior order occur gene- 

 rally in basins, one side of which is at present open towards 

 the sea, and even where the basin form is not obvious, as in 

 the strata which lie on the two slopes of the Apennines, it 

 may be inferred from other circumstances. 



94. This order is easily distinguished by its organic remains, 

 which differ totally from those of the supermedial and lower 

 orders, while its more regular stratification, and the inclined 

 position of its layers, mark its difference from the formations 

 of the modern period. 



95. The superior order may be divided into three groups, 

 which are styled Pliocene, Miocene, and Eocene. These 

 are distinguished by the characters of the shells of mollusca, 

 which they contain imbedded. In the pliocene formations, a 

 large proportion of the shells, say more than half, belong to 

 existing species. In the miocene, the proportion of existing 

 species is less than half, while in the eocene, the number of 

 existing species is small. By far the greater part of the 

 shells in all the three groups belong to genera, either iden- 

 tical or closely analagous to those now living. 



96. In the superior order of France and England, many 

 of the species which at present exist, are not now found in 

 the neighbouring seas, but in those of warmer climates, and 

 where the species still exist in the neighbouring seas, the 

 fossil shells are usually larger. This would prove that the 

 climate of those countries was warmer when the superior 

 order was deposited, than at present. This is also confirmed 

 by the vegetable i*emains, which, although of extinct species, 

 are analagous to those of tropical climates. 



97. Each group is composed of two formations, one of 

 which has been deposited from fresh, the other from salt 

 water. 



