THEORIES OF WERNER AND BUTTON. 



349 



which they have once evidently covered, is also a phenomena of fre- 

 quent occurrence ; and its exj3lanaiion must be sought from some of 

 the same causes, that have excavated valleys. This appearance of 

 the strata is called a denudation. 



The first of the above theories is that of Werner : he supposed 

 that all the matter of which primary, transition, and secondary rocks 

 are formed, was originally held in solution by water, and that the 

 water, so saturated with mineral matter, covered the whole globe. 

 The primary rocks of granite were formed by chemical precipitation, 

 and their peaked summits and declivities were the result of their ori- 

 ginal deposition. On the steep sides of these primary mountians were 

 subsequently deposited the different schistose rocks, and all the sec- 

 ondary strata. During the time that these rocks were depositing, 

 the water, though nearly saturated with mineral matter, was capa- 

 ble of supporting animal life, and the shells and remains of zoophytes 

 and fish, were enveloped in the strata, at the period of their deposi- 

 tion. According to this theory, when the water retired from the pres- 

 ent continents, the mountains and valleys were already formed. 



The theory of Werner requires for its support the admission of con- 

 ditions, which appear in the present state of our experience impos- 

 sible, and it is at variance with existing phenomena. The vertical 

 position of beds of puddingstone, sandstone, and, the tertiary strata 

 in the Alps, could not have been their original one ; nor can the 

 bendings and contortions of the strata, so common in Alpine coun- 

 tries, be explained by original deposition. A further account of part 

 of Werner's theory is given, Chap. IX. p. 148. Werner's theory of 

 valleys is altogether distinct from that theory which ascribes the for- 

 mation of valleys to inequalities of the surface, subsequently enlar- 

 ged by the erosion of water. 



The second theory, that all valleys have been excavated by the 

 rivers that flow through them, was maintained by Dr. Hutton and 

 Professor Playfair : it formed a part of their general theory of the 

 earth ; the leading propositions of which are, that the surface of the 

 present continents is wearing down by the action of the atmosphere 

 and by torrents, and that the materials are carried by rivers into the 

 sea, and there deposited. At a future period, these materials will be 

 melted or consolidated by subterranean heat under pressure of the 

 ocean, and subsequently, by the expansive force of central fire, the 

 bed of the ocean will be elevated, and form new^ continents. Accor- 

 ding to this theory, our present continents have been also formed from 

 the ruins of a preceding world, and elevated by a similar cause. It 

 is only with that part of the Huttonian system, which relates to the 

 excavation of valleys, that we have at present any concern. 



It is remarkable, that a theory which maintains that the continents 

 were raised from the ocean by subterranean fire, should limit the for- 

 mation of valleys to the action of the rivers that run through them ; 

 for if the land were raised by an expansive power acting from be- 



