Ti Outlines of Geology. 



Certain limestones, red sandstone, coal strata, lias, and chalk, 

 and some other sandstones, belong to this division. 



Lastly, we find depositions of sand, gravel, and clay, of the 

 bones of quadrupeds, accumulations of peat, and some other 

 substances now in progress of accumulation or deposition, which 

 are included under the term alluvial formations. 



The fifth class contains the produce of volcanic fires, and of 

 more partial combustions. So that under one or other of these 

 classes, or formations, as they are theoretically called, it is sup- 

 posed that the various substances occurring amongst our rocks 

 and strata may be included. It would be premature, to descant 

 upon or criticise this theory, without more particular notice of 

 the facts upon which it rests, and of those which militate against 

 it, than I now can lay before you ; but I think that you will 

 hereafter, when in the possession of details, find me borne out 

 in asserting, that it is, in all points, weak and unsatisfactory. 

 That the very idea of an universal solvent, and of crystalline, 

 succeeded by mechanical deposits, is at variance with all expe- 

 rience or analogy; in short, that it includes an unwarrantable 

 accumulation of hypotheses, assigning opposite qualities to the 

 same agent ; and that, like most of its predecessors, it is equally 

 at variance with nature, and with itself — " in a word, that it is 

 a system which might pass for the invention of an age when 

 sound philosophy had not as yet alighted on earth, nor taught 

 man that he is but the minister and interpreter of nature, and 

 can neither extend his power nor his knowledge a hair's breadth 

 beyond his experience and observation of the present order of 

 things." 



The Plutonic theory, as it is generally though not quite pro- 

 perly termed, owes its origin to Dr. Hutton, and proceeds upon 

 principles differing from those of the ancient Vulcanists, at the 

 head of whom we may place Whitehurst, and entirely at vari- 

 ance with the leading tenets of the School of Freyburgh. It 

 has been defended by the late Mr. Playfair, under the term of 

 the Huttonian Theory, and his " Illustrations" rank among the 

 •most eloquent of scientific compositions ; not but that he some- 



