I A 



34 CKOLOGICAL STRUCTURE OF THE 



immense portion of the valley of the Mississippi, 

 over which we have in the preceding section rapidly 



glanced, without entering into details, exhibits 

 throughout all its extent unequivocal marks of a 

 pelagian origin, its rocks are filled with marine pro- 

 ductions, with bivalve shells, with Alcyonites, En- 

 crinites, Madrepores, Millepores, Tubiporites, Flus- 

 tras, Trilobites, some species of Ammonites, Zoo- 

 phytes, &c. &c. of which by far the greater part are 

 now extinct, having disappeared with the ocean that 

 gave them birth ; indeed, several of their genera no 

 longer possess any existing type. The antiquity of 

 this order of things, apparently anterior to the crea- 

 tion of any other organized beings, is beyond our 

 comprehension ; what occasioned the reflux and sub- 

 sidence of these mighty waters, and the consequent 

 elevation of the land, is a subject equally involved 

 in mystery. It is sufficient for us to mark the 

 different epochs of this reflux, so as to connect 

 our remarks, and render them intelligible to those 

 who wish to follow, us in the course of observa 

 tion. 



The pelagian calcareous rock which occupied 

 our attention in the preceding section, and which 

 may correctly be termed a compact limestoue, pre- 

 sents to ouv view scarcely any of those shells and 

 marine productions still existing in the present ocean. 

 They are almost without exception bivalves, among 

 which the 'erebratulites continually predominate. 

 Coal, petroleum, fluor spar, blende galena, argilla- 



