THE GEOLOGIST. 



63 



T have here to request that, for the present at least, it may be 

 taken for granted that the beds or strata are presented in regular series 

 or succession, containing the remains of ancient animals and plants, 

 which have been of very different characters, at those different periods, 

 or systems, into which the past history of our own planet is divided. 



Probably many of my readers will have acquired much of this 

 elementary information from the numerous popular treatises which 

 have been produced by so many of our eminent geologists, although 

 there are BtUl many to whom even these primary tenets of our science 

 will be new. Eor their sakes, therefore, I repeat that which I know 

 to be familiar to others. 



Even those who know the general features of the science will not 

 suffer by a repetition occasionally of the knowledge they have acquired, 

 and as never an artist who sits down to draw an oft-repeated scene pro- 

 duces a fac-simile of his predecessors' works, so the geologist, though he 

 repeats an old tale, still embodies something of his feelings and of 

 himself in the new picture which he paints. The accompanying tables 

 will display the principal divisional arrangements of the various earths 

 or rocks, and will aid tho uninitiated reader in following our remarks. 



UNSTlLiTiriED EOCKS. 



Plutonie. 



Rocks subjected to heat be- 

 neath the surface and not 

 ejected like lava, although 

 often protruded in rugged 

 masses through the disrupt- 

 ed beds of stratified rocks. _^ 



I Volcanic. 

 Rocks the produce of 

 ancient volcanos ; often 

 Example: 'ejected as in modern 

 Granite, eruptions. 



Examples — Basalt, Trap, 

 Lava, 



STEATIFIED EOCKS. 



Rocks formed by the deposition from water of the sediments derived 

 from pre-existing materials. These are grouped into great divisions 

 called systems, representing periods in time, the rocks thus associated 

 together having a collactive relationship. The members of each group, 

 while presenting also some general linking features among themselves, 

 are nevertheless marked by distinctive characters which more or less 

 separate them from each other. 



