DYNAMICAL GEOLOGY. 297 



conceptions of geologists regarding the structure of mountain- 

 systems altered as their knowledge of stratigraphy increased ; 

 the stages of progress may be judged by a comparison of the 

 text-books of geology published in the successive decades of 

 the nineteenth century. 



The text-books of the Wernerian School were mostly 

 ignorant of the complicated structure of mountain-systems ; 

 inclined strata were assumed to have originated in the inclined 

 position. Their teaching on structure was based exclu- 

 sively upon observations in plains, hill districts, and mines. 

 Geological sections of mountains and plains appear in the 

 work of Conybeare and Phillips, and an ideal section of 

 the earth's crust in Buckland's Text-book of Geology (1836) 

 became the model for a number of similar attempts. Lyell's 

 Principles and Elements of Geology, like the majority of the 

 text-books in the first half of the nineteenth century, treated 

 the structural relations of the earth's crust somewhat meagrely. 

 Naumann, in his Lehrluch der Geognosie (1850), was the 

 first author who devoted a special chapter to " Geo-Tectonics," 

 and he comprised in it practically everything which had been 

 established in this domain of geology. 



As the interest in tectonical relations developed, the 

 questions of the earth's configuration began to be studied 

 from a more intelligent standpoint. Previous centuries had 

 offered only speculative literary matter on this subject. Steno 

 certainly had as early as 1669 appreciated the fundamental 

 doctrines of configuration ; upon the basis of his own re- 

 searches in Tuscany, he had explained the forms of mountains 

 and valleys as the results partly of crust compression and 

 fracture, partly of the upheaval of stratified deposits, partly 

 of the accumulation of volcanic material. Descartes, Leib- 

 nitz, and Buffon attributed the origin of ocean-basins, con- 

 tinents, and mountain-system^ to fracture and wrinkling of 

 the solid crust, and to withdrawal of the surface waters into 

 subterranean cavities. Hooke, Vallisnieri, Lazzaro Moro, 

 Needham, and others thought volcanic forces had upheaved 

 the continents and mountain-systems. 



Inthrows, subsidences, wrinkling of the crust in virtue of 

 the earth's contraction, and upheaval by subterranean forces 

 have long been recognised as the principal factors in 

 determining surface conformation, and re-appear in modern 

 theories with various modifications and applications. 



