FAT HUE OJT THE FORMATIONS. 377 



SECTION III. 



Nature of the Rocks Relative Age and Superposition of the Formation* 

 Primitive, Transition, Secondary, Tertiary, and Volcanic Strata. 



THE preceding section has developed the geographical 

 limits of the formations, the extent of the direction of the 

 zones of gneiss-granite, micaslate-gneiss, clay-slate, sand- 

 stone, and intermediary limestone, which come successively 

 to light. We will now indicate succinctly the nature and 

 relative age of these formations. To avoid confounding 

 facts with geologic opinions, I shall describe these forma- 

 tions, without dividing them, according to the method 

 generally followed, into five groups primitive, transition, 

 secondary, tertiary, and volcanic rocks. I was fortunate 

 enough to discover the types of each group in a region where, 

 before I visited it, no rock had been named. The great 

 inconvenience of the old classification is that of obliging 

 the geologist to establish fixed demarcations, while he is 

 in doubt, if not respecting the spot or the immediate super- 

 position, at least respecting the number of the formations 

 which are not developed. How can we in many circum- 

 stances determine the analogy existing between a limestone 

 with but few petrifactions and an intermediary limestone and 

 zechstein, or between a sandstone superposed on a primi- 

 tive rock and a variegated sandstone and quadersaudstein, 

 or finally, between muriatiferous clay and the red marl of 

 England, or the gem-salt of the tertiary strata of Italy ? 

 When we reflect on the immense progress made within 

 twenty-five years, in the knowledge of the superposition of 

 rocks, it will not appear surprizing that my present opinion 

 on the relative age of the formations of Equinoctial America 

 is not identically the same with what I advanced in 1800. 

 To boast of a stability of opinion in geology is to boast of an 

 extreme indolence of mind ; it is to remain stationary amidst 

 those who go forward. What we observe in any one part of 

 the earth on the composition of rocks, their subordinate 

 strata, and th? order of their position, are facts immutably 



