100 THE CAMBRIAN. [bull. 81. 



moD.s'8 stratigraphic work was correct, M. Barrande credited him wit! 

 having correctly located the Primordial fauna in America. 



In 1861 Prof. Hall changed the reference of the Georgia trilobites 

 from the Hudson River group to the Quebec group. 1 In a letter writ 

 ten to M. J. Barrande, dated April, 1862, the explanation of this is given. 

 He states that his own conviction was that the Red sandrock aw 

 the Granular Quartz of Vermont were of the age of the Potsdam sand- 

 stone and that tbe schists and shales which held the trilobites belong 

 between the Potsdam sandstone and the Trenton limestone. He thus 

 changed his views in relation to the age of the rocks containing Ole- 

 nellus and other trilobites, and referred them to the lower portion ol 

 what is now designated as the Silurian (Ordovician). He says : 



You will understand, then, that if my views touching the relations of these rocks 

 are exact the valley of the Hudson River from the high lauds on the south of Lak€ 

 Champlain, save a small u limber of inconsiderable exceptions, is occupied by rocks 

 of the Primordial zone, that is, by rocks placed between the Potsdam sandstone an( 

 the Trenton group. Thus the Hudson River group in its typical localities belongs 

 the Primordial period. 2 



In explaining how he came to adopt the view that the trilobites froi 

 the Georgia slates of Vermont and those described by Dr. Emmons 

 from the black slates of Washington County belonged to the Hudsoi 

 River group, together with the strata in which they were contained, hi 

 says : 



I wish to claim nothing for myself or for my former views, for we owe the tins 

 solution of this question to the Canadian survey. Yet there remain some divergent 

 views in regard to the relation between the shales and the Potsdam sandstone. 



He further states that this arose from his seeing the Potsdam sand- 

 stone run beneath the slate at Whitehall, New York, and a number 

 other places ; that at no point where the Potsdam sandstone is seen if 

 there any shale or other formation beneath it, excepting the crystalling 

 rocks of the Adirondacks. Speaking of the " Granular Quartz," he say 

 that it presents the same relation as the Potsdam sandstone to th< 

 schistose rocks ; that he has always referred it without hesitation to the 

 Potsdam sandstone. He held the view that the schistose rocks, witl 

 their impure sandstones, brecciated limestones, and calciferous san< 

 rock, are to be placed between the Potsdam sandstone and the Trentoi 

 limestone group; that the relation of this group of schists or slates tj 

 the Potsdam sandstone seems to be that of an upper formation. Ii 

 none of the outcrops that he saw in the disturbed region east of the 

 Hudson was there one that could explain the phenomena presented, on 

 the supposition that the sandstone is the upper rock. He then quotes 

 the nomenclature of Eaton to show that it was almost the same as that 

 finally adopted by the Geological Survey of New York, that is, the order 

 of superposition of the formations, the "Granular Quartz" being placed 

 at the base. It is also stated that the graptolites found in the beds 



Correction for the thirteenth annual report. 14th Ann. Rep., State Can. Nat: Hist., 1861, p. 110, 

 2 Letter on the Primordial of America. Soc. jjeol. France, Bull., 2 e ser., vol. 10, 1862, p. 732. 





