STUDY OF THE GRAPTOLITES. 219 



Tlir. — GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION OP THE GRAPTO- 

 LITES IN THE ROOKS 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 Silu- 

 rian system. In this respect, the horizon of the Graptolite beds corres- 

 ponded with those of Ireland, from which these fossils bad 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. 

 Barrande 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 published information 

 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 

 Europe 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 (supposed to belong 

 to the same family) 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 indica- 

 tion of the occurrance 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; 

 and although it was shown that the graptolites were all of different species 

 from those previously described, yet they appeared to offer only corrobo- 

 rative evidence in support of the previously entertained opinion regarding 

 the age of the strata. It was only at a later period, and from the dis- 

 covery of numerous other fossils in the same formation, some of them 

 having a primordial aspect, that its higher antiquity was suspected. 



* Geological Report on Londonderry, etc., page 817-322. 



