1852.] LOGAN POTSDAM SANDSTONE FOOT-PRINTS. 213 



part lettered a there is also ripple-mark. It is an inch or two below 

 5, and the ripple-ridges. on it run N. 15° E. The inference which I 

 wish to draw from these facts is, that the ripple-ridges on succeeding 

 surfaces, only a few inches above one another, being in different di- 

 rections, and the limit of the producing cause of the ripple being in- 

 dicated in one example, it appears probable that the ripple was pro- 

 duced by tide rather than by a current in deep water ; that in the 

 same area one part of the surface was dry when the wave was acting 

 close by on another part; and that the direction of the wave was 

 towards the apex of the triangular space. 



The fourth area, of which no plan is given, is removed a few yards 

 to the east of that lettered C in PI. VII., and on the casts of this sur- 

 face it will be seen that there are ten tracks, measuring — 

 ft. in. in. 



6 



long by 



5y wide. 



10 6 



>5 



5* „ 



8 







5 „ 



2 5 







5* „ 



5 9 







H „ 



2 7 







4i „ 



6 9 







5i „ 



5 7 







5i „ 



4 8 







4 



4 







5 „ 



56 5 



The geological importance given to these tracks by the opinion 

 expressed by Professor Owen in regard to the specimens produced 

 last season, has induced me to spare no pains in bringing evidence to 

 bear on the subject ; and the materials having been submitted to the 

 examination of the Professor, he has kindly undertaken to lay before 

 the Meeting a description of them. 



At the Evening Meeting, March 24, M. E. Desor exhibited an 

 engraving of a slab with Foot-prints bearing a general resemblance 

 to Protichnites. These Tracks are from the vicinity of the Niagara 

 Falls, and belong to the " Clinton group." Prof. Owen has supplied 

 the following note on these Foot-prints. 



The plate exhibited by M. Desor gives a view of a series of prints 

 on each side a median track, of about 18 inches in extent. The 

 foot-prints on one side of the median track are in successive groups of 

 three prints, the two next the track being most approximated. Only 

 the pairs of prints corresponding to those median pairs are shown on 

 the other side of the track. The plate gives no indication of succes- 

 sive groups of three sets of prints ; but it would be unsafe to rely 

 upon it for the precise character of the impressions. 



[Note. — The casts of surface A, PI. VIII. (including the tracks, P. 

 7-notatus, P. lineatus, and P. alternans), together with characteristic 

 impressions of the remaining species, will be deposited in the British 

 Museum.] 



