Geology. — On the Order of Succession of Rocks. 345 



cessible to them, and because we believe there are already more 

 geological readers in our overspreading language than in any 

 other, and that the proportion will greatly increase. 



To our uninitiated readers, we think it due to offer a short his- 

 tory of one of those subdivisions of the geological scries, which we 

 have connected with our tabular view. Primary, transition, se- 

 condary, and tertiary. For an account of the first, we refer them 

 to our last number, page 293, which contains our reasons for 

 substituting the term primary, for primitive. The rocks, 1 to 4 

 inclusive, are those comprehended in the primary division ; they 

 have hitherto been found entirely composed of inorganic matter; 

 whether because organized vegetable and animal beings had not 

 been produced, when these rocks were first consolidated ; or whe- 

 ther because the igneous origin of the greater part of these rocks 

 was inconsistent with the preservation of organic forms. 



In the early periods of the history of Geology, all rocks were 

 divided into primitive and secondary ; the evidences of organic na- 

 ture being entirely confined to this last and most numerous 

 branch. This last division being evidently too cumbrous, could not 

 escape further subdivision ; and it being observed that the lowest 

 rocks in the secondary portion contained the first and the sim- 

 plest forms of organized bodies, the lowest portion of the se- 

 condary got the name of transition, as if at the period of the 

 consolidation of these rocks, the planet was in a state of transition 

 from inorganic to organic matter. The exact line where the 

 transition begins, and where it ends, has not yet been agreed 

 upon universally. Those slates which are subordinate to the 

 transition limestone, are considered, by geologists, as containing 

 the first organic remains, none having yet been found in the ser- 

 pentine, the talcose rocks and slates ; or the hornblende rocks 

 and calcareous deposits, which are superincumbent in the series 

 to the primary. The English geologists have limited the extent 

 of the transition to the graywacke. No. 7, inclusive ; whilst the 

 continental geologists would include in it the old red sand stone, 

 the carboniferous limestone, and some of them even the coal 

 beds. As this difference in opinion may, perhaps, at no very dis- 

 tant day, be reconciled by the oblivion into which the transition 

 itself may fall ; and as it is a question of organic remains, some- 

 what of a speculative nature, from the imperfect examination 

 those rocks have received, we shall content ourselves with the 



Vol. I.— 44. 



