208 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



attention to the erosion effected by running water, their re- 

 searches lacked a scientific basis. Guettard had already laid 

 hold of the main principles of ablation and erosion when he, in 

 1774, set forth the "degradation" of mountains and the whole 

 earth surface. Targioni also explained surface conformation 

 upon true principles ; while Eber was such an ardent believer 

 in Guettard's views that he drew accurate panoramas of the 

 Swiss Alps in order that posterity might be enabled to recognise 

 subsequent changes in surface conformation. On the other 

 hand, De Maillet and Buffon attributed the excavation of 

 valleys to the action of submarine currents during the retreat 

 of the ocean and the emergence of islands and continents. 

 These views were afterwards upheld by Cuvier, De Saussure, 

 and Werner, and recur in some measure in the early editions 

 of LyelPs Principles. 



Pallas thought the destruction of mountains and the forma- 

 tion of valleys was associated with intermittent local floods, 

 and this explanation found favour with Buckland, Sedgwick 

 (1825), Daubeny (1831), Elie de Beaumont (1829), and many 

 others. This theory gave support to the "diluvialists," who 

 taught that the Mosaic flood was the final and grandest event 

 in a series of inundations, and that which had mainly shaped 

 the present surface conformation of the globe. It is interesting 

 to remember that Buckland introduced the term denudation 

 to express the scouring and hollowing of the continents which 

 he attributed to the action of a universal flood. 



But the more natural principles inculcated by Guettard and 

 Targioni steadily made their way as the number of geological 

 observations increased. Hutton and Playfair, by their admir- 

 able treatment of the subject, opened up this field of research 

 upon scientific lines. In France and England, during the 

 early decades of the nineteenth century, Montlosier and 

 Poulett-Scrope explained the origin of many valleys solely as 

 a result of the erosive activity of streams, and this was the 

 view supported by Von Hoff and Kiihn in Germany. In 1829 

 Murchison and Lyell together wrote an essay " On the Excava- 

 tion of Valleys," in which they showed their appreciation of 

 the potency of river erosion. This explanation then came to 

 be currently accepted ; at the same time it is freely admitted 

 that many valleys owe their primary origin to tectonic causes. 



Lyell was the first to investigate the work done by erosion 

 within a definite period of time. Upon the basis of the 



