TRANSACTIONS OF THE SECTIONS. 185 



ceratite limestone of Sweden and Russia, and in the Graptolite shales. Mr. Hall, 

 the best American authority, states that the Caradoc sandstone is zoologically an 

 equivalent of the Hudson River group. While the Matinal series in New York 

 has afforded more than 250 forms, and the Bala group 122, there are, according to 

 the late Mr. Sharpe's comparison, only 12 in common. M. de Verneuil, contrasting 

 the American and North Europe Matinal fossils, finds only 14 in common. Still the 

 two faunas, though so poor in cosmopolite forms, have so many identical genera 

 that there can be no hesitation in admitting them to be the products of the same age. 

 Of the 20 species common to the American Matinal limestones and Matinal shales, 

 10, according to Mr. Sharpe, are also European species. This is one among many 

 facts showing that the most widely distributed races were those which best withstood 

 the revolutions betweea one formation and another. Adding together the British and 

 the North European species, there are only 24 or 6J per cent, found also in the Ame- 

 rican basin. 



Levant Series {Medina Group). — Passing the important horizon which divides the 

 Matinal from the Levant strata, we find that the latter, produced in an age of much 

 crust disturbance, contain a very limited fauna and flora, and seem not to be repre- 

 sented in Europe, but to have been formed in America just prior to the Wenlock 

 period of Great Britain. 



Surgent and Scalent Series (or Clinton and Niagara). — While the Surgent series 

 contains more than 100 well-defined species, 12 of them are ascertained to be Euro- 

 pean, and are eminently distinctive of the British Wenlock strata. But this Wen- 

 lock formation is equally a representative of the Scalent or Niagara of the United 

 States. The two together contain more than 326 species, the Surgent about 104 ; 

 the Scalent some 222. Only 15, that is to say about 5 per cent., are common to both ; 

 but according to Hall, the Wenlock and its European continental equivalent has, at 

 least, 35 Niagara species. Thus we perceive that the Surgent and Scalent groups 

 are severally in closer affinity with the Wenlock of Europe than with each other. This 

 instructive fact suggests, that, during the quiet deposition of the Wenlock beds, an 

 important crust-movement may have occurred within the Appalachian basin, alter- 

 ing the conditions suitable to its marine inhabitants. The dissimilar areas which the 

 Surgent and Scalent deposits occupy indicate such a shifting of the Appalachian sea- 

 bed. These facts indicate that we cannot proceed securely in the classification of 

 formations until .we synchronize them widely. 



Premeridian Series (Lower Helderherg) . — In the region of New York, where this 

 formation has been most closely examined, it has furnished Mr. Hall more than 200 

 species, only about 9 per cent, of which are also European, being fossils of the Wen- 

 lock and Dudley strata ; but Mr. Hall thinks that this number of identical forms will 

 be increased on a more critical comparison. Only two or three of the species, namely 

 the Calymene Blumenbachii, Atrypa reticularis, &c., occur in any higher or lower 

 stratum. Though thus insulated by its species, it is linked to the adjoining forma- 

 tions by possessing with them many common genera. While palseontologically it 

 has so little in common with the strata above and beneath it, it curiously enough 

 finds more than a tenth part of its organic remains in distant European formations, 

 in the Wenlock especially. This anomaly disappears, however, when we reflect on 

 the superior magnitude of the crust-movements or changes of physical geography 

 which seem to have taken place in the Appalachian sea. Compared with those in 

 the Silurian basin, Mr. Hall, agreeing with Mr. Sharpe, regards the lower Helderberg 

 strata as representing the Wenlock formation of England, while M. De Verneuil 

 considers them equivalent to the Ludlow. Hall admits the propriety of recognizing 

 the Niagara on the one side, and the Lower Helderberg on the other, as of Wenlock 

 age. 



Meridian Series (Oriskany) . — This formation is still more completely insulated 

 from the formations above and beneath it, than any of the preceding. Its fossils, 

 not numerous, are exclusively its own, though they possess features linking them 

 somewhat with those of the next higher formations. Most American geologists, 

 adopting the view of their synchronism, first proposed by M. De Verneuil, regard 

 them as the base of the American Devonian deposits. We shall see, however, that, 

 though nearly on this horizon, no precise coordination of any of the middle palaeo- 

 zoic strata of the two basins is practicable. 



