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 Graptolitideaef . 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 Paloeontology 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 figiired in the first volume of the Pala5ontoIogy of New-York, the 

 Graptolitet textani, G.furcatus, G. terraiulus, Cgraci/i* 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 Palfflontology of New-york, Vol. ii, p. 174. 



