XVI INTRODUCTION. 



The equivalents of these shales, etc., in the western States, 

 were also, for the same reasons, referred to the Hudson river 

 group. 



The discoveries of the last few years, however, chiefly made 

 hy the Canadian Geological Survey, have gradually developed 

 the fact that the New York geologists (excepting Dr. Emmons*) 

 had made a great mistake in placing the true Hudson river 

 rocks above the Trenton: or in other words, that these rocks 

 are older than the Trenton, and belong to the Primordial zone 

 of Barrande. Consequently the slates and shales alluded to 

 farther west, in New York, and their equivalents in the western 

 States, cannot be properly referred to the Hudson river group. 

 In a note on this subject, published in the Report of the Wis- 

 consin Survey (pages 443 to 445), Prof. Hall, after speaking 

 of the great number of Primordial types of fossils found in the 

 Hudson river group in Canada, and some of the adjoining 

 States, within a few years past, makes the following remarks : 



* * * a ^y e are therefore satisfied, from the geological rela- 

 tions of the great mass of these rocks, and from the contained 

 organic remains, that they are of older date, and that the fossils 

 of newer age occurring in limited localities should not be re- 

 garded as characterizing the formation ; that the great mass ot 

 the Hudson river rocks, in their typical localities, are older 

 than the Lorraine shales and sandstones of Pulaski, etc.; and that 

 the term Hudson river group cannot be properly extended to 

 these rocks, which, on the west side of the Hudson river, are 

 separated from the Hudson river group, proper, by a fault not 

 yet fully ascertained." 



"There can be no propriety," he continues, "in transferring 

 the name Hudson river group from its typical locality, and 

 applying it to rocks we now know to be of younger age, and 



* It is well known that Dr. Emmons had long maintained, against a vigorous and not 

 always over courteous opposition, that the Hudson river group proper holds a lower 

 stratigraphical position than had been assigned it by his collaborators of the New 

 York Survey. 



