52 CANADIAN FOSSILS. 
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 Bohe- 
mia and Scandinavia; while their association with primordial fossils in 
the Malvern Hills and at Snowdon, indicated the earlier appearance of 
these zoophytes in Great Britam. 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 in 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 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 Lévis, 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. 
The shales of Point Lévis, with their associated limestones and sand- 
stones, since termed the Quebec group, are now regarded as embracing 
the period from the Calciferous sandstone to the Chazy limestone, inclusive. 
This epoch therefore is entirely anterior to that of the Hudson River 
formation, and a careful comparison of all the species of graptolites has 
shown that no identical species occur in the two series of rocks. 
In the present state of our knowledge, we recognize the Graptolitidee 
as beginning their existence at the period of the Potsdam sandstone. 
The greatest development of the family, both in genera and species, is 
