96 The Founders of Geology LECT. 



The former of these two branches of research naturally 

 came to be pursued first. It is by far the more obvious 

 of the two, and considerable progress had to be made in 

 it before the very possibility of the second line of enquiry 

 could be recognized and pursued. 



We have seen that with all his sagacity and insight, 

 Guettard gave no indication that he had any ideas as to 

 the chronological relations of the various groups of strata 

 which he included in his "bands." Neither he nor 

 his contemporaries ventured to draw geological sections. 

 "We have found that even De Saussure and Pallas, 

 though they saw that the rocks of the central parts of 

 mountain-chains are older than those of their flanks, did 

 not definitely express their ideas on this subject in graphic 

 form. Desmarest had clearly perceived the evidence for 

 a long sequence of volcanic eruptions in Central France, 

 but he never applied this evidence towards an elucidation 

 of the general history of the globe. Yet as far back as 

 the time of Guettard, the first seeds had been sown which, 

 before the end of the century, were to germinate in so wide 

 an expansion of geological theory. 



I propose in the present lecture to trace the history of 

 the idea of geological succession during the latter half 

 of last century. In that time it was advanced more 

 particularly by three observers, Lehmanu, Fuchsel, and 

 Werner. 



The earliest definite statements as to a recognisable order 

 among the rocks of the earth's crust are to be found in a 

 treatise by Johann Gottlob Lehmann (died 1767), published 

 at Berlin in 1756. It is a little duodecimo volume, roughly 

 printed on poor paper, extending to 240 pages, and bearing 



