©F THE EARTH'S SURFACE. 147 



been advanced in support of the diurnal formation of the val- 

 ley in which this lake lies, granting that it has been excavated 

 by the diurnal actions, since these granitic blocks were deposi- 

 ted upon Mount Jura ; it still remains to be explained, how 

 the lake of Geneva itself was formed, the depth of which 

 amounts in some places (Saussure, art. 44.) to 950 feet. Now, 

 as has very fairly been stated, this lake is constantly receiving 

 all the spoils of the district which lies above it, called the Val- 

 lais, yet delivers nothing at Geneva, situated below it, 

 but pure water. It is evident, then, that every known diur- 

 nal action tends to fill up this lake, and none to excavate it. 

 This is therefore admitted by Mr Playfajr, to be a case " in 

 u which hypothetical reasonings are warranted by the strictest 

 " rules of philosophical investigation, and where we must 

 *' therefore have recourse to an agent that is invisible." Illu- 

 strations of the Huttonian TJieory, p. $66. 



This acknowledged difficulty seems calculated to entitle the 

 following speculations to a patient hearing from this gentle- 

 man ; and he has already, in another part of the same work, 

 expressed himself with regard to them, and other kindred opi- 

 nions, in a manner highly encouraging to discussion, and which 

 affords one of the most striking examples of candour that has 

 ever occurred. 



" These arguments," Mr Playfair says, (referring to those 

 he had just been stating) art. 367. page 412. " appear to me 

 " conclusive against the necessity of supposing the action of 

 " sudden and irregular causes on the surface of the earth. In 

 this, however, perhaps I am deceived, neither Pallas nor 

 Saussure, nor Dolomieu, nor any author who has espoused 

 the hypothesis of such causes, has explained his notions 

 with any precision ; on the contrary, they have all spoken 

 " with such reserve and mystery, as seems to betray the weak- 



T 2 " ness, 



