429 



SECONDARY LIMESTONE. 



IT was formerly remarked, that the primary 

 limestones bore a very small proportion to the 

 other strata with which they are associated. In 

 the secondary class, on the contrary, the space 

 occupied by the calcareous strata is very great, 

 whether we consider the thickness of the beds, 

 or the extensive tracts of country in which they 

 are found to be the predominant rocks. 



The great importance very properly attached 

 by geologists to many of the secondary limestones 

 might have appeared to justify a separate des- 

 cription of some of these, instead of thus treating 

 of the whole under one general head. But the 

 present plan, as in that of the sandstones, was 

 not adopted without ample consideration of the 

 subject, and till after a full conviction of the im- 

 possibility of forming any other arrangement, 

 without producing unnecessary repetitions, and 



