30 



Forty-second Annual Report on the 



On the Track of an Animal Lately Found in the Potsdam Formation. 

 By Sir W. E. Logan, F. K. S. 

 [Read before the Natural History Society of Montreal, June, I860.] 



" The Potsdam sandstone is recognized in Canada and New York as 

 the base of the Lower Silurian series. As far as we are certain of 

 the formation in the province it rests unconformably upon the 

 Laurentian series; but on the north shore of Lake Huron, the 

 Huronian series supports unconformably a sandstone which has 

 been supposed to be Potsdam; as no fossils, however, have been met 

 with in it there, its equivalence is somewhat doubtful, particularly as 

 the superior fossiliferous rock into which it passes, appears to be the 

 Bird's-eye and Black Biver group. 



"Mr. Barrande in a paper communicated to the Geological Society 

 of France about a year ago, compares the Potsdam formation with the 

 Primordial Zone, and appears disposed to unite it with the strata 

 marked by Paradoxides near Boston in Massachusetts, and Placentia 

 Bay in Newfoundland, the first locality yielding Paradoxides Harlani 

 which he identifies with his P. spinosus and the latter Mr. Salter's 

 P. Bennetii, and probably other allied genera and species. But while 

 no well ascertained Primordial species .have been met with in the 

 Potsdam of Canada and New York, the formation appears in Canada 

 to be rather allied to the strata above than those below it.* 



"Li the Potsdam of Canada and New York, independent of fucoids, 

 the number of species of which the forms have been either wholly 

 or partially preserved is only three. Two of them are Lmgulce named 

 by Hall L. prima and L. antiqua; and while these so far resemble one 

 another that they might by some palaeontologists be considered 

 variety of one species, we in Canada have a Lingula (L. Belli of Bill- 

 ings), in the Chazy, which might almost be considered another variety 

 of the species, the x^eculiarity of them all being the length and sharp- 

 ness of the beak. In Canada there is also found in the Potsdam the 

 impression of a spire of a large flat Pleurotomaria, which so strongly 

 resembles the spire of P. Laurentiana (Billings) of the Calciferous, 

 that they can scarcely be distinguished. In addition to these uj)ward 

 affinities in the only preserved forms, there are beds of passage 

 between the Potsdam and Calciferous formations, in which the 

 strongly marked distinctive lithological characters of the two are well 

 preserved, and at St. Timothy on the Beauharnois Canal those beds of 



* Since this paper was read, it has been ascertained by Mr. Billings, that the trilobites 

 found in the Potsdam at Keeseville, New York, and presented by Mr. Dana at the meet- 

 ing of the American Association at Montreal, in 1857, belong to Conocephalus, one of the 

 genera characterizing the Primordial Zone in Bohemia. 



