178 



Contributions to Palceontology. 



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 already 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 West- 

 ern 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 fragment- 

 ary condition, it may ultimately turn out that the discovery 

 of more perfect individuals may establish relations which 

 are not at present apparent. I am authorized to say, how- 

 ever, that Sir William E.Logan is still disposed to regard 

 some of the trilobites of the Quebec group as occuring in 

 masses which may have been derived from a somewhat 

 older formation, and imbedded in these strata at the time 

 of their deposition. 1 



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 



1 Geology of Canada, 1863, p. 860. 



