On the Track of an Animal, Sfc. 279 



AKT. XXXIX. — On the Track of an Animal lately found in the 

 Potsdam Formation, By 8ir W. E. Logan, F.R.S. 



{Read before the Natural History Society of Montreal, June, 1860.) 



The Potsdam sandstone is recoornised 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 up- 

 on 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 of the Bird's-eye and Black River group. 



Mr.Barrandein a paper communicated to the Geological Society 

 of France about a year ago, compares the Potsdam formation 

 ■vsdth the Primordial Zone, and appears disposed to unite it 

 with the strata marked by Paradoxides near Boston in Massa- 

 chusets, 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 proba- 

 bly 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.* 



In 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 Lingulce, named by Hall L. prima^ and L. antiqua ; and 

 while these so far resemble one another that they might by some 

 palaeontologists be considered varieties of one species, we in Cana- 

 da have a Lingula [L. Belli of Billings,) in the Chazy, which might 

 almost be considered another variety of the same species, the peculi- 

 arity of them all being the length and sharpness of the beak. In Can- 

 ada there is also found in the Potsdam, the impression of the spire of 

 a large flat Pleurotoniaria^ which so strongly resembles the spire of 

 P . Laureniiana (Billings) of the Calciferous, that they can scarcely 



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

 that the trilobites found in the Potsdam at Keesville, New York, and 

 presented by Mr. Dana at the meeting of the American Association at 

 Montreal in 1857, belong to Conocephalus, one of the genera character- 

 izing the Primordial Zone in Bohemia. 



