INTRODUCTION. 
15 
In Canada, however, have been made the greatest accessions to our 
knowledge of the fossil forms of this period. In certain localities, the slates 
of the higher part of the group have yielded large numbers of graptolites, 
in such a state of preservation as to show, for the first time, the true 
structure of this fossil. The specimens heretofore figured and described, 
prove to be for the most part mere fragments or single rays, which, se¬ 
parated as they usually are in the rock, give no true idea of the form and 
mode of growth of the original animal. The extensive collections made in 
Canada, besides giving this information, furnish some ten or twelve new 
species*. 
In addition to the graptolites, several new species of Didyonema occur 
in the same shales, in such associations and in such condition as to prove 
very conclusively the truth of the suggestion that this genus should be 
placed among the Graptolitidesef. The same collections likewise furnish 
two additional genera belonging to this family. 
The opinions advanced by the writer in 1844 and 1845, and published 
in the first volume of the Paleontology of New-York, relative to the age 
of the rocks composing the metamorphic belt on the east side of the 
Hudson river, and including the principal part of the Green mountain 
range, has been fully confirmed by Prof. Adams in the Geological Reports 
of Vermont. A re-examination of some portions of the same belt has 
added fresh evidence of the age of the formations, so far as included in 
Eastern New-York, Western Massachusetts, and Vermont. 
In the Canada Survey, also, this problem has been wrought out with a 
care and accuracy in the details which lead to the greatest certainty, not 
only in the general result, but equally in reference to individual members 
of the group. In this region, which is an extension of the Green mountain 
range to the northward, the formations acquire an enormous development, 
* Among the species described and figured in the first volume of the Palaeontology of New-York, the 
Graptolites sextans, G.furcatus, G. serratulus, G. gracilis and G.bicornis are almost the Only species 
that indicate the mode of arrangement of the parts; and these species alone could never have given us a 
true idea without farther discoveries. 
t Palaeontology of New-York, Vol.ii, p. 174. 
