AND ANALOGIES, OF ROCKS. 225 



these be rocks actually fused, or strata merely in- 

 fluenced ; and this also being uniform, under grada- 

 tions, the results should correspond. 



Such substances as diallage rock, and serpentine, 

 or rocks which are essentially characterized by such 

 minerals as hypersthene and augit, are the real ex- 

 ceptions to this simplicity, and they are but a few in 

 the total system; while, with perhaps no exception, 

 being the produce of perfect fusion, it is less difficult 

 to comprehend why they should have formed this 

 breach in the general simplicity which I have thus 

 attempted to establish. 



Although it has here been inculcated that all the 

 stratified rocks which are not the produce of animals, 

 have ultimately been derived from former rocks, and 

 probably, in a series of succession, the limits of which 

 we cannot pretend to conjecture, it is still proper to 

 remark, that there is a progressive change of character 

 as we retreat. The limestones, it has been particu- 

 larly shown, become more rare, but the argillaceous 

 substances diminish also; so that, at length, in arriving 

 at that antiquity which, to our observation, is the 

 highest, siliceous rocks predominate in a great degree. 

 Thus a certain philosophy might extend the con- 

 clusion formerly suggested with respect to the in- 

 crease of calcareous strata, and imagine an universe 

 once as incapable of maintaining vegetables, as it has, 

 to all appearance, been limited in the numbers and 

 nature of its animals; a desert of rocks and sand. 

 But this conclusion is not justified when we take a 

 general view of all the phenomena which geology 

 presents. That it has been drawn, has arisen, either 

 from false theories or partial views. If the siliceous 

 substances predominate in the more antient parts of 

 the series, it must be remembered that these are but 



vot. i. Q 



