INTRODUCTION. 
xix 
on the Continent. Again, Mr. Logan has shown, from his collections in Canada, several 
European species not yet detected in New-York or farther westward, which still more 
assimilate the eastern and western extremities of these formations so widely separated by 
the Atlantic. 
In commencing our examinations, we find that marine plants are coeval with the earliest 
created animal forms ; and that both appear, though obscurely, in the same rock. 
Throughout the entire series of the lower division, each rock or group appears to be typified 
by a few peculiar forms of this class, which are cpiite as much restricted in their geological 
range as are those of animal life. 
Among the lower classes of animals we find an absolute identity in many of the species, 
and a remarkable similarity in several others. We can hardly refuse to believe that our 
Graptolite shales are of the same age as those of England, Ireland or Sweden, when we 
find so many identical species in the two formations; and though we here have many not 
yet recognized in those countries, some of them will doubtless be found there on further 
examination. The Chcctetes petropolitanus of Russia is probably the same with our C. 
hjcoperdon , which likewise occurs in the Caradoc sandstone of Britain.* Nearly all the 
other Corals of this period, however, are new or undescribed. 
Among the Crinoidea, most" of the forms appear to be quite new, and to present even 
generic characters unknown in the higher rocks. We are able to recognize, nevertheless, 
the occurrence of the family Cystidea, in a species of Echino-encrinites allied to the E. 
angulosus. Those singular forms, the Spharonites, have not yet been discovered in (his 
country ; and though abundant in Sweden and Russia, have only recently been recognized 
in England.! We shall doubtless yet discover the same fossil in this country, though it is 
not probable that it will ever become characteristic of the strata. We find that animals of 
this order commenced their existence among the earliest forms, and as soon as calcareous 
matter formed any considerable portion of the deposit. 
Of the Brachiopoda, we have several identical and many allied species in the different 
genera. The Lingula quadrata is clearly identical with the Russian species; and another 
species which we find in our Trenton limestone, is apparently the same as the L. attenuata 
* This fossil is often referred to Favosites fibrosa, which is regarded as having a great geological range. In our 
Trenton limestone species, connecting foramina are never visible; while in the similar form in the Pentamerus and 
Delthyris shaly limestone, there is no difficulty in distinguishing them. I have not recently examined good specimens 
from the Clinton and Niagara groups, but am at present inclined to express some doubt as to the identity of the species 
in that rock and the Trenton limestone, and the statement on page 67 may be received with some allowance. 
f See Geology of Russia in Europe and the Ural Mountains, Vol. i, p. 38. The facts in relation to the discovery of 
Cystidea in England, there made known, had escaped my observation at the time I wrote my description oi Echino- 
encrinites, and translated the passages from the second volume of the same work. 
