210 SIXTEENTH EEPORT ON THE CABINET OF NAT. HISTORY. 



SUPPLEMENTARY NOTE ON THE POTSDAM SANDSTONE. 



When I commenced this paper, I had intended to confine myself 

 strictly to the description of fossils in my collection from the 

 sandstone of the Upper Mississippi valley, and a comparison with 

 those previously described from that region of country. 



I have not desired to depart from this course ; and I have al- 

 ready said that it formed no part of my plan to compare these 

 western forms with those of more eastern localities, which have 

 been obtained in the older rocks of Canada and Vermont, and 

 brought out in the publications of the Canadian Survey. I cannot, 

 of course, have failed to perceive a similarity of form between 

 some of the Western Trilobites, and those from the Quebec 

 group ; though I believe there is not specific identity in any of 

 them. Should such identity be proved hereafter, the latter would 

 of course have prior authority in the nomenclature. There has 

 been no opportunity for a comparison of the fossils of these two 

 regions ; and those of both being in a fragmentary condition, it 

 may ultimately turn out that the discovery of more perfect indivi- 

 duals may establish relations which are not at present apparent. 

 I am authorised to say, however, that Sir William E. Logan is 

 «till disposed to regard some of the trilobites of the Quebec group 

 as occurring in masses which may have been derived from a 

 somewhat older formation, and imbedded in these strata at the 

 time of their deposition.* 



In making a comparison between fossils of the Quebec group, 

 as developed in Newfoundland, on the one hand, and in several 

 localities in Eastern Canada on the other, it is remarked that 

 while there is a general resemblance between the faunas of the 

 two extremes, "the Newfoundland rocks have none of the Trilo- 

 bites, such as CONOCEPHALITES, DiKELOCEPHALUS, MeNOCEPHALUS, 



and others which give to a small portion of the Point-Levis series 

 a primordial aspect."f 



The western species are all from a sandstone of well authenti- 

 cated position and relations with the superincumbent rocks, but 

 of moderate thickness as compared with the Potsdam and Quebec 

 groups of Canada, Vermont and Newfoundland ; and we do not 

 yet know the character and fossils of the lowest beds of the 



• Geology of Canada, 1863, p. 860. f Geology of Canada, p. 263. 



