STUDY OF THE GRAPTOLITES. 253 



VIII. Geological and GeographAcal Distribution of the Gn'aptoUtes in the 

 Rocks of Canada and the United States. 



Until the remarkable discovery of the graptolites of Point Levis, in 

 1854, the chief repository of these fossils known in American rocks was 

 in the shales of the Hudson River valley. The position assigned to the 

 rocks of this valley was the superior part of the lower division of the 

 Silurian system. In this respect, the horizon of the Graptolite beds 

 corresponded with those of Ireland, from which these fossils had been 

 described by General Portlock ; * and with the position assigned to those 

 in Sweden, as well as with those of the Llandeilo and Caradoc formations 

 of Great Britain. The Graptolites of Bohemia are from strata referred 

 by M. Babrande to the base of the superior division of the Silurian 

 system ; and those of Saxony were regarded as from the same horizon. 



In 1850, M. Barrande expressed the opinion that the epoch of the 

 graptolites was posterior to that of the " Faune Primordiale " in Bohemia 

 and Scandinavia ; while their association with primordial fossils in the 

 Malvern Hills and at Snowdon, indicated the earlier appearance of these 

 zoophytes in Great Britain. A comparison of all the pubhshed informa- 

 tion on the subject at that time induced M. Barrande to conclude, as a 

 general fact, that the graptolites had made their earliest appearance in 

 the regions of the northwest; and that their highest development 

 in central Em-ope had only been reached at a later period, or at the base 

 of the upper division of the Silurian system. 



The investigations during the Geological Survey of New York had 

 proved in a pretty satisfactory manner that no graptolites proper occurred 

 above the horizon of the Clinton group, though Dictyonema had been 

 found in the Niagara formation. The species, at that time known 

 ranged, from the higher strata of the Lower Silurian, to the lower beds 

 of the Upper Silurian division; and both in Europe and America, these 

 fossils were regarded as of eminently silurian character, and unknown 

 in any later geological periods. 



The discovery of a graptolitic species in the Potsdam sandstone of the 

 St. Croix River valley, by Dr. H. A. Prout, in 1850, was the first indi- 

 cation of the occurrence of this family of fossils at a lower horizon than 

 that of the Hudson river and Trenton formations. 



Before the discovery of graptolites in the shales of Point Levis, these 

 rocks were supposed to belong to the age of the Hudson river formation ; 



* Geological Report on Londonderry, etc., page 317-322. 



