1852.] LOGAN POTSDAM SANDSTONE FOOT-PRINTS. 199 



striati ; apertura semilunaris, labio interno plicis tribus spiralibus, externo intus 

 octo instructo ; umbilicus maximus. Long. O-J^ unc, lat. 0^^ unc. 



Found by Edward Alexander, Esq. 



The following species also, liitlierto unfigured, are represented in 

 Plate V. :— 



Helix bilamellata, Sowerby. Plate V. fig. 8. From a spe- 

 cimen found by Mr. Blofeld. 



Helix spurca, Sowerby. Plate V. fig. 10. From a specimen 

 found by Mr. Alexander. 



BuLiMUS FOSSiLis, Sowerby. Plate V. fig. 4. From a specimen 

 in the Museum of the Geological Society. 



BuLiMus TEREBELLUM, Sowcrby. Plate V. fig. 5. From Mr. 

 Darwin's examples in the cabinet' of Sir Charles Lyell. 



BuLiMUS SUBPLICATUS, Sowerby. PlateV. fig. 6. From a spe- 

 cimen found by Mr. Blofeld. 



March 24, 1852. 



The following communications were read : — 



1. On the Foot-prints occurring in the Potsdam Sandstone of 

 Canada. By W. E. Logan, Esq. F.G.S. 



[Plates VI. to VIII.] 



Since the reading of the paper communicated to the Society last 

 year on the track and footsteps of an animal in the Potsdam Sand- 

 stone of Lower (East) Canada*, the lowest member of the Lower 

 Silurian rocks, farther investigation by my assistants on the Provin- 

 cial Survey and myself have brought to light a considerable number 

 of similar tracks in the same rock ; and, although quite convinced in 

 my own mind of the age of the rock, the importance attached to 

 these impressions has induced me to search for additional evidence 

 on the point, in order that others as well as myself might be satisfied 

 that no mistake had been made in regard to it. 



In my previous paper it was stated that a sandstone formation, 

 resting unconformably on a metamorphic series of gneiss and inter- 

 stratified limestone, and occupying a narrow strip at a variable 

 distance on the north side of the St. Lawrence, swept round from 

 the valley of this river to that of the Ottawa, the turn forming an 

 obtuse angle and occurring on the Riviere du Nord : that a similar 

 rock, proceeding from Keesville in New York, turns from the Valley 

 of Lake Champlain to that of the River St. Lawrence, and, forming 

 at the bend a sharper angle, is projected out across Beauharnois 

 towards the previously mentioned bend in a long tongue of sandstone, 

 pierced near the extremity by Mont Calvaire, a protruding mass of 

 * Quart. Journ. Geol. Soc. vol. vii.p. 247 etseq. 



