PRINCIPLES OF GEOLOGY. 9 



often crystallized rocks, variously associated and related to one another, 

 commonly stratified at high angles of declination, and for the most part 

 destitute of organic remains. Such are granite, gneiss, mica slate, quartz 

 rock, primitive limestone, serpentine, and slate. From the Shetland Isles 

 to Cornwall, a general conformity in character unites the mountain 

 groups. From these elevations, the rocks above-named dip or decline on 

 all sides into the earth, sink deep under the more level regions, and are 

 there covered up and buried beneath various deposits of limestone, sand- 

 stone, coal, clay, chalk, and other strata of inferior hardness, and not 

 crystallized, but amply stored, nay filled to admiration, with plants, 

 corals, shells, and other remains of organized beings. Besides these, 

 there is a third division of rocks ; viz. sienite, porphyry, basalt, &c. 

 which are of local occurrence, appear in peculiar forms, and present 

 particular phenomena. They repose indiscriminately upon the rocks of 

 the mountains or those of the plains, and occasionally divide them by 

 dykes, yet have only an accidental connexion with either. Such is the 

 general character of the geology of Britain. And I may appeal to the 

 progress of the science for proof, that such is the general character of 

 the whole face of the earth. 



In every country the great mountain ranges are composed of the 

 lowest rocks with which we are acquainted. There may be other rocks 

 below the granitic series, but we have not yet found means to observe 

 them. Therefore, as being the lowest, and consequently the most ancient 

 rocks, included in the compass of our observation, we call them Primary. 

 Those more horizontally deposited rocks which fill wide plains, and rest 

 upon the subterranean slopes of the former series, composed of various 

 alternations of calcareous, siliceous, and argillaceous substances, with 

 local deposits of coal, and generally abounding in shells and other organic 

 remains, are universally termed Secondary. Those rocks which rest 

 indiscriminately on the primary or the secondary series, lie in irregular 

 patches, and send off veins or branches into both primary and secondary, 

 being in fact superadded to both, yet conjoined to neither, receive the 

 name of Independent or Overlying. 



c 



