600 HISTORY OF GEOLOGY. 



theories. The great problem which offers itself 

 here, in reference to geology, is, to examine the 

 value of any hypotheses by which it may be at- 

 tempted to explain the succession of different races 

 of animals and plants jn different strata; and though 

 it may be difficult, in this inquiry, to arrive at any 

 positive result, we may at least be able to show 

 the improbability of some conjectures which have 

 been propounded. 



I shall now give a very brief account of some of 

 the attempts made in these various departments of 

 this province of our knowledge ; arid in the present 

 chapter of inorganic changes. 



Sect. 2. Aqueous Causes of Change. 



THE controversies to which the various theories of 

 geologists gave rise, proceeding in various ways 

 upon the effects of the existing causes of change, 

 led men to observe, with some attention and per- 

 severance, the actual operation of such causes. In 

 this way, the known effect of the Rhine, in filling 

 up the lake of Geneva at its upper extremity, was 

 referred to by De Luc, Kirwan, and others, in their 

 dispute with the Huttonians; and attempts were 

 even made to calculate how distant the period was, 

 when this alluvial deposit first began. Other modern 

 observers have attended to similar facts in the na- 

 tural history of rivers and seas. But the subject 

 may be considered as having first assumed its proper 

 form, when taken up by Mr. Von Hoff ; of whose 



