STRATIGRAPHICAL GEOLOGY 429 



he assumes nothing further regarding the rocks comprised in a 

 "Terrain" than that they originated during a definite great 

 geological period. The "Terrains" are then sub-divided in 

 Formations or Groups. Each Formation is said to contain 

 rocks that had been formed under similar or almost identical 

 conditions ; and the Formations are again divided into Sub- 

 Formations (Sous- Formations}^ each of which is said to com- 

 prise a complex of strata conformably succeeding one another, 

 and having the same fossil fauna or flora. The most valuable 

 part of Brongniart's work is the large number of lists enumerat- 

 ing the characteristic fossils in the sub-formations. 



The Terrains are classified under two Periods, the Periode 

 Jovienne, with the three youngest, and the Periode Saturnienne, 

 with the other six Terrains. 



D'Omalius d'Halloy partly accepted Brongniart's terminology, 

 partly altered it, but he followed the sub-division and general 

 arrangement of the Terrains. The Belgian geologist was 

 Brongniart's solitary disciple in the literature. In comparison 

 with the contemporary work in Great Britain, Brongniart's 

 stratigraphical system could only be regarded as a retrogressive 

 step. 



The excellent Geological Manual of De la Beche (London, 

 1831) followed the example of W. Smith, Conybeare and 

 Phillips, and adopted their terminology and their arrangement 

 of the formations. That De la Beche showed a special interest 

 in the modem and diluvial formations was only what might 

 have been expected in the author of the Geological Observer. 

 In his treatment of the "Group above the Chalk," De la Beche 

 made use of the literature on the Tertiary formations of the 

 Paris basin, Italy, Switzerland, and the other Tertiary basins 

 of Europe, but in spite of the rich material in the literature he 

 failed to construct a precise, chronological table of the succes- 

 sion. For the Cretaceous group, the English sub-divisions are 

 taken as a type; in the Oolitic group, De la Beche made 

 only one or two slight alterations on W. Smith's sub divisions, 

 and, on the basis of the important works of Merian and 

 Thirria, assigned the Jurassic formations of the Swiss and 

 French Jura to their proper position in the stratigraphical 

 succession. De la Beche included in the group of the "Red 

 Sandstone " the whole series of Keuper, Muschelkalk, Bunter 

 Sandstone, Zechstein, Copper Slate, and Red Underlyer. In 

 the Carboniferous formation he embraced very rightly only the 



