NATURE OF SUPPOSED FOSSIL TRACKS. 487 



evidently more or less fragmentary, but many of them are continuous 

 over lengths of nine or ten feet ; and in places they run in different 

 directions, and occasionally cross one another. 



The track-like aspect of these impressions is so striking, that any 

 attempt to cast doubt on their animal origin may seem altogether 

 futile. The fact that no crustacean remains (or other vestiges of 

 animals by which they could have been produced) have been dis- 

 covered in connection with them, is, of course, of no moment : as 

 undoubted foot-tracks of reptiles and birds occur in the Connecticut 

 Valley, and elsewhere, under similar circumstances. There is one 

 point, nevertheless, and I think a strong point, which militates 

 against their animal origin. The latei"al indentations or supposed 

 feet-impressions vary in number, as regards their grouping, in different 

 " tracks," thus forcing Professor Owen to establish no less than four 

 distinct species : Protichnites multinotatus, P. octonotatus, P. septem- 

 7iotatus, and P. altemans, with a provisional species, P. lineatus, to 

 include the track without lateral pit-marks.* The association of so 

 many different species, if the supposed tracks be really of animal 

 origin, is at least a very remarkable cii-cumstance : one, indeed, 

 that might cause doubt in unprejudiced minds as to the real nature 

 of these impressions. But, if not the tracts of crustaceans or other 

 animals, to what, it may be asked, can these impressions be due 1 I 

 would suggest, but with all due apology for the heresy of the sugges- 

 tion, that they may be nothing more than the impressions of large 

 fucoids. Many of the existing Melanospermai grow to a great length : 

 and in many genera with flattened or riband-like fronds there is a 

 well-defined midrib, sufficiently hard to make a distinct indentation 

 when the frond is pressed on damp sand. The lateral indentations 

 of our Potsdam impressions may have been made by groups of spores 

 or sori arranged (as seen in many existing forms) along the sides of 

 the frond. If it be said that the sori in existing fucoids could scarcely 

 accomplish this, it would not be more unreasonable to infer that in 

 these ancient sea-weeds the spores were of a somewhat harder or 

 denser nature, than to have to admit with Professor Owen that the 



* It may perhaps be urged that these species collectively are only intended to be provisional : 

 the names applying not to the animals, but simply, as terms of convenience, to the "tracks." 

 But if some of these impressions were really made by a crustacean with seven pairs of feet, 

 whilst others were made by crustaceans having eight pairs, Ac, they must certainly have 

 been made by distinct, even if by closely related, species : using the term species in its con- 

 ventional or commonly understood sense. In the Crustacea, and indeed throughout the animal 

 series generally, the number of the feet or legs, as a distinctive character, is especially definite. 



