of North Ameiica with those of Europe. 49 



type when the dorsal lobe, instead of being simple, is divided by 

 a small medial saddle. 



The distribution of the Productus, offers another remarkable 

 coincidence. Unknown in America in the Silurian system, ap- 

 pearing under one or two small forms in the Devonian epoch, the 

 species assume in the carboniferous rocks a development altogether 

 in harmony with the facts observed in Europe. The Spirifers of 

 this epoch present also in America the character of "having the 

 plications often dichotomous, which M. d'Archiac has already 

 indicated in Europe,* and by which they are distinguished from 

 those of the Devonian epoch, which have them always simprie.f 



As to the Terebratulce, we will mention the interesting fact of 

 the simultaneous disappearance of two species, the T. reticularis 

 and T. asp era, which, during the Devonian and upper Silurian 

 epochs, were spread with great profusion from the Altai and Ural 

 to the Missouri. We will cite also, as simultaneous phenomena 

 upon the two continents, the appearance of those Crinoids form- 

 ing a passage to the echinoderms, such as the Palctechinus or 

 Melonites, the extinction of those great corals, such as the 

 Favosites Gothlandica, Porites intcrstincta, &c., and their re- 

 placement by the Chcetetes and Lithostrotion, nearly identical in 

 Europe and in America. The analogy between the two conti- 

 nents continues even to the Foraminifera and the plants. We 

 have seen indeed that the Fusulinm cylindrica, so characteristic 

 of the carboniferous limestone of Russia, occurs in the cherts or 

 siliceous beds of the coal sandstones of Ohio. And as to plants, 

 the immense quantity of terrestrial species identical on the two 

 sides of the Atlantic, proves that the coal was formed in the 

 neighborhood of lands already emerged, and placed in similar 

 physical conditions. 



With the Carboniferous system terminates the palaeozoic forma- 

 tion in North America. During all the time of its deposition, the 

 surface was free from great disturbances. J Slow and insensible 

 oscillations had caused to emerge areas more or less circu- 

 lar of the submarine surface where the Silurian and Devonian 

 deposits were made, and had contracted the limits of carbonife- 

 rous deposits ; but the horizontally of the beds was not disturbed. 

 11 is only after the carboniferous epoch that an energetic force, 



Memoir on the PalaBOz. Foss. (Trnns. Geol., vol. v, page 319.) See also Geo!- 

 °gy of Russia in Europe, vol. ii, p. 126. Von Buch, in his interesting memoir 

 *BiCli he has published upon Cherry Island (Btiren inset), has insisted with reason, 

 °n the importance of this character'which might be thought insignificant. 



fit is also only at the Devonian epoch that we rind the Spirifers ia which the 

 back is divided by a slight furrow, as in 5. mucronatus and Bouckouli. 



♦ In the eastern part of the United States, where the palaeozoic formation is 

 m «ch disturbed and metamorphosed, Mr. H. D. Rogers believes he is able to re- 

 th g u Ze tfaces of ^locations, which have broken up the strata after the epoch of 

 fte Hudson River or Clinton Group. (This Journal, ii ser., vol. i, p. 411.) 



Secokd Ser,i S) Vol. VII, No. 19.-Jan., 1849. 7 





