INTRODUCTION. 143 



Wernerian school already recognised most of the questions 

 which are at present treated in text-books. 



Considerations of the earth's physiography, dynamical 

 geology, petrography, geogeny, and architecture or tectonic 

 structure were fairly familiar ground at the time; the great 

 difference is in the teaching of the chronological succession of 

 the rock formations. Modern geology gives pre-eminence to 

 the accurate determination of the age of the rocks, stratum by 

 stratum, according to the contained fossils ; Werner's disciples 

 were satisfied with an approximate conception of the relative 

 age of whole formations, and scarcely associated the study of 

 historical succession of organised creatures with any geological 

 interest or value. 



In France, three distinguished pupils of Werner wrote text- 

 books upon the basis of his teaching Brochant de Villiers ( 1 800), 

 De Bonnard (1819), and De Voisins (1819). The Treatise of 

 Geognosy, published by D'Aubisson de Voisins, won wide popu- 

 larity on account of its clearness and the elegance in its mode 

 of treatment. Like Reuss, D'Aubisson held closely to the 

 methodical arrangement of the subject introduced by Werner 

 in his lectures, so that the general arrangement of these two 

 text-books is very similar; but the French author took his 

 illustrative examples chiefly from French geology, Reuss from 

 German districts. In common with most of Werner's 

 disciples, D'Aubisson de Voisins made many blunders in 

 respect of the Secondary formations. He united Alpine 

 limestones (Tri.-Jur.-Cret.), the limestones of the Jura chain, 

 the Magnesian limestones (Permian) and Liassic limestones 

 of England and the German Zechstein (Permian) in one group 

 that of the Older Secondary limestones; and treated as 

 Younger Secondary limestones, contemporaneous with German 

 Muschelkalk, the Jurassic calcareous strata of France, the 

 Forest Marble and Cornbrash, and Portland stone of England 

 (Middle and Upper Jurassic), the Solenhofen lithographic 

 stone (Upper Jurassic), and the fish-shales of Monte Bolca 

 (Mid-Eocene). 



An important deviation from Werner's teaching was made 

 by D'Aubisson in his insertion of Tertiary formations between 

 the Secondary deposits and diluvial clays and gravels. 

 According to D'Aubisson, the Tertiary series included the 

 deposits of the Paris basin (now grouped as Eocene and 

 Oligocene), so clearly elucidated by Brongniart and Cuvier ; 



