166 



Mr. Desor exhibited some of the proof-sheets of the 

 illustrations to Messrs. Foster and Whitney's Report of the 

 Geological Survey of the Mineral lands of Lake Superior. 

 Among them was the representation of a slab of singular 

 character, from the Clinton group at Green Bay. 



It was a question, whether the markings upon it were the 

 remains of a fossil body or the track of some animal. It had 

 been maintained at the session of the American Association for 

 the advancement of science at Albany, that it could not be the 

 former, as there was no trace of animal substance or change in 

 the grain of the stone. It had been suggested that it was the 

 track of some marine worm with many feet. Mr. Desor himself 

 thought it was more likely to have been made by an animal with 

 four feet, possibly a reptile, although it was a matter of great 

 doubt. Mr. Whitney had observed that the distance from the 

 central groove to the outer edge of the double row of impres-^ 

 sions on each side of it was greater at one end than the other, so 

 that the whole impression was somewhat wedge-shaped, and 

 he was therefore led to the conclusion that it could not be a 

 track. 



Dr. Cabot remarked, it was possible that the marks at one end 

 might have been made by a different part of the foot from those 

 at the other. 



Prof. Rogers said, that Mr. Whitney and himself had found by 

 measurement, that the distance from the central groove to the 

 inner edge of the lateral markings at one end of the slab was to 

 the distance at the other as two to one ; the distances to the 

 outer edge being as three to two. This would seem to be an 

 objection to the theory of its being a track. Another difficulty 

 was the perfect regularity of interval between the lateral mark- 

 ings. It could hardly be supposed that the track of an animal 

 with many feet could be made without some blurring of the first 

 prints by the succeeding ones. Mr. Whitney had suggested that 

 it might be the impression of a skeleton. 



Dr. Gould remarked, that the impressions, if produced by a 

 walking animal, would have been alternate ; if by a leaping 

 animal, the tracks of the short legs which receive the plunge 

 would have been deeper than the others, which is not the case. 



