SILURIAN" ROCKS OF BOHEMIA. 665 



history provinces existed at those very remote times in Scandinavia, 

 Bohemia, England, and the United States. 



Of Trilobites, 27 species have been found in Bohemia in these "pri- 

 mordial" beds, 71 in Scandinavia, 12 in America, and 10 in England, all 

 referable to the same group of genera, but not one in a hundred of the 

 species being common to the difterent areas. The doctrine of the uni- 

 versality of a primeval fauna, once so popular, is thus completely and 

 forever overthrown. If it still lingers in the minds of some paleontolo- 

 gists, it is pi'obably because of the wide range of certain plants of the 

 carboniferons era. But besides that every day demonstrates this case to 

 be exceptional, it has also become more and more evident that the appar- 

 ent anomaly is caused partly by the predominance in that ancient flora 

 of ferns and Lycopodiacese, orders of which the living species are dif 

 fused over as wide a space, and partly by the abundance of plants like 

 the Sigillaria3, of which there are no living analogues. There is no 

 proof that the coniferse of the carboniferous era had a more extensive 

 range than the living species of the same class. 



Not only in the earliest known paleozoic epoch has M. Barrande now 

 shown that distinct assemblages of species inhabited separate regions, 

 but also that the same law prevailed in as marked a degree dui-ing the 

 tim^es of his second and third faunas, or when rocks of the age of the 

 Lower and Upper Silurian of England were formed. At these periods, 

 not only peculiar species of Crustaceans, but Cephalopods also, and 

 other mollusks, as well as corals, flourished; one set in Bohemia, an- 

 other in Scandinavia, and others in the several great regions before 

 enumerated ; in a word, wherever these ancient strata have been care- 

 fully studied. 



But if separate portions of the earth have at every former era been 

 simultaneously peopled by distinct sets of marine species, owing to 

 variations in climate, in the depth of the sea, the mineral nature of its 

 bottom, or by reason of the position of continents and the larger islands, 

 and many other conditions in the organic and inorganic worlds, there 

 must at every former period have been points Avhere distinct zoological 

 provinces were parted from each other by abrupt and narrow barriers, 

 resembling the Isthmus of Suez or the Isthmus of Panama. It is well 

 known that a distinct marine fauna now prevails on each side of those 

 narrow belts of land, and it is evident that a slight subsidence of the 

 earth's crust, to the amount of only a few hundred feet, could cause one 

 host of species to invade the tenitory of another ; and it might, there- 

 fore, have naturally been asked, whether there are any signs of such 

 invasions having been eff'ected during those reiterated upheavals and 

 subsidences to which geology bears testimony. M. Barrande has fur- 

 nished us with a distinct and satisfactory answer to this question, for he 

 has detected near the upper limits of the Lower Silurian strata of Bohe- 

 mia (in his Hage D.) an intercalated and lenticular-shaped mass of fos- 

 siliferous rock, containing organic remains, almost all of them specifi- 

 cally identical with fossils found in the overlying Upper Silurian 



