32 THE GEOLOGICAL HISTORY OF PLANTS. 



their indefinite forms, their want of nodes or append- 

 ages, and their markings being always of such a na- 

 ture as could be produced by scratches of a sharp 

 instrument. Since, however, fishes are yet unknown in 

 beds of this age, they may possibly be referred to the 

 feet or spinous tails of swimming crustaceans. Salter 

 has already suggested this origin for some scratches of 

 somewhat different form found in the Primordial of 

 Great Britain. He supposed them to have been the 

 work of species of Hymenocaris. These marks may, 

 however, indicate the existence of some free-swim- 

 ming animals of the Primordial seas as yet unknown 

 to us. 



Three other suggestions merit consideration in this 

 connection. One is that Algae and also land-plants, drift- 

 ing with tides or currents, often make the most remark- 

 able and fantastic trails. A marking of this kind has 

 been observed by Dr. G. M. Dawson to be produced by 

 a drifted Laminaria, and in complexity it resembled the 

 extraordinary \2Enigmichnu8 multiformis of Hitchcock 

 from the Connecticut sandstones. Much more simple 

 markings of this kind would suffice to give species of 

 Eophyton. Another is furnished by a fact stated to the 

 author by Prof. Morse, namely, that Lingulae, when dis- 

 lodged from their burrows, trail themselves over the 

 bottom like worms, by means of their cirri. Colonies of 

 these creatures, so abundant in the Primordial, may, 

 when obliged to remove, have covered the surfaces of 

 beds of mud with vermicular markings. The third is 

 that the Rhabdichnite-markings resemble some of the 

 grooves in Silurian rocks which have been referred to 

 trails of Gasteropods, as, for instance, those from the 

 Clinton group, described by Hall. 



Another kind of markings not even organic, but alto- 

 gether depending on physical causes, are the beautiful 

 branching rill-marks produced by the oozing of water 



