184 REPORT — 1856. 



logue of British Fossils, there are restricted to the strata below the break 136 

 genera, and to those above it 149, while there are 74 genera common to the two 

 sets. In other words, the proportion of common to restricted is nearly 26 per cent. 

 Turning now to the American older and middle palseozoic faunas, I find, on care- 

 fully comparing Hall's catalogues of the fossils of the two corresponding sets of 

 formations (deficient, unfortunately, in any enumeration of Premeridian or latest 

 Silurian species), that there are restricted to 



the Primal ■» 



„ Auroral I 53 genera, 



„ Matinal J 

 while there are restricted to 



the Levant "| 



„ Surgent > 81 genera ; 



„ Scalent J 



and that there are 37 genera common to the two series, the whole number of genera 

 being 171. Here the proportion of common to restricted is about 25 per cent. The 

 introduction of the Premeridian fossils, many of which are on the horizon of the 

 Wenlock beds of Britain, would add materially to the proportion of genera not held 

 in common, and would reduce the common to probably less than 20 percent. Thus 

 even on this broadest basis of comparison, there would seem to have been a much 

 more complete extinction and replacement of organic types in North America, than 

 occurred in Europe, or at least, in Britain. 



Parallelism of the North American and European Palceozoic Rocks. 



Having examined the reciprocal relations of the Appalachian palaeozoic strata, and 

 also those of the European palaeozoics among themselves, as expressed by the nume- 

 rical proportions of their fossils, and also by the generic forms of their organic re- 

 mains, and learned where the stream of life was most continuous, and where most 

 interrupted, it remains to coordinate the deposits of the two basins with each 

 other. Thus may we hope to learn what formations are synchronous, and what are 

 without equivalents. In attempting this correlation, it should be remqpibered that 

 Nature presents no true or literal equivalency of strata, nor anything closer than a 

 mere approximate relationship where the deposits compared belong to independent 

 basins, or even to the remote sides of the same great receptacle. The most we can 

 hope to establish, is a general agreement in time with possibly a stricter synchronism 

 of the few chief paroxysmal movements which agitated the bed of the ancient ocean. 

 Partially representative formations are discoverable, but equivalent ones are not to 

 be looked for upon any philosophical view, since the distribution of organic beings 

 is essentially partial or geographical. The life horizons of the globe are no more 

 universal than are its horizons of sedimentation. With these reservations, we turn 

 to the degrees of affinity, linking the American and European palaeozoic groups of 

 fossils. 



Relations of the Primal Series {Potsdam sandstone) . — The Appalachian Primal strata 

 characterized by a peculiar group of Trilobites, absent from the higher formations 

 and by those earliest brachiopodous genera, Oholus, Lingula and Orbicula, are 

 obviously nearly on the horizon of Barrande's Primordial zone, and of the lowest 

 rocks of Russia and Scandinavia- Notwithstanding a general agreement of type, 

 there is not a species common to the two continents. 



Auroral Series (Calciferous, Chasy and Black River Gi-oups). — The Appalachian 

 Auroral strata, containing in New York alone more than 83 recognized forms, possess 

 but a single species, the Lituites convolvens, in common with the strata which repre- 

 sent them in Europe. Hall thinks that the Auroral limestones are not represented 

 by any British rocks, nor clearly by any European. Possibly they were approximately 

 contemporaneous with the Swedish Orthoceratite limestone. 



Matinal Series (Trenton and Hudson River Groups). — This group of formations, 

 Matinal limestone (Trenton), Matinal black slate (Utica), and Matinal shale (Hudson 

 River), would seem, from the testimony of the fossils, to be represented in Great 

 Britain by the Llandeilo flags and Caradoc sandstone, or more generally by Sedg- 

 wick's Bala or Upper Cambrian group. It finds also a near equivalent in the Ortho- 



