235 



CHAP. XXXVL 



Secondary Limestones. 



IT was already remarked, that while these limestones 

 occupy a considerable space in the secondary scries, 

 the waste of the previous rocks will account for the 

 arenaceous and argillaceous strata which unite with 

 them to form it, under the shape of sandstones and 

 shales, but that in comparing the proportion of pri- 

 mary limestone with that of the secondary, the waste 

 of the former rock could not have produced the enor- 

 mous quantity of the latter. Another source was 

 therefore to be sought, and that was shown to be the 

 action of living animals. 



As the primary limestones alternate with the other 

 associated strata, throughout the whole series, so the 

 secondary extend through the entire class to which 

 they appertain. Occupying also considerable tracts 

 on the surface, they form the basis of extensive plains, 

 and constitute many remarkable ridges of hills through- 

 out the world; thus ranging from the lowest situa- 

 tions, as in England, to very high elevations, as in 

 Jura and the Apennine. 



If even it were within my plan to describe the cha- 

 racters of every rock and every series, everywhere, it 

 would have been difficult, or rather impossible, to 

 have attained such an object; while, in the present 

 case, this difficulty is particularly felt. Our accounts 

 of the calcareous tracts of the earth are especially 

 defective; while the term transition, with the mistak- 

 ing of secondary for primary limestones, has produced 

 great confusion. It is but recently that we have ac- 

 quired definite ideas, even respecting those of Europe; 

 and, to this hour, many of them are involved in ob- 



