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GEOLOGY. 



Unidentified forms. — Besides the forms that can be identified 

 there are some which cannot be interpreted with certainty. Among 

 these are certain tracks found in Canada, Wisconsin, and elsewhere. 

 Two varieties are illustrated in Fig. 125. They consist of consecutive 

 rows of V-like forms with trail markings superposed, as though fila- 

 ments or flexible organs were dragged over the impressions imme- 

 diately after they were formed. The organs that made the V-like 

 impressions were flexible, as shown by the variation in the form of 



Fig. 125. — Unidentified forms. Tracks of an unknown animal found in the Upper 

 Cambrian sandstone near New Lisbon, Wis. 



the tracks, the curvature of the ridges, and the shifting of the posi- 

 tion of the apex. The depth of the impressions and the compacting 

 of the surface of the sand implies a rather heavy animal, or one that 

 burrowed beneath the sand. The nature of the animal that produced 

 them is problematical. There are other impressions that consist of 

 rows of indentations, as though made by the feet of arthropods, while 

 still others are continuous grooves. 



Implied life. — Scientific geology, in the strict sense of the term, 

 contents itself with considering the demonstrable forms and their 



