616 



SIE J. W. DAWSON ON BTJRROWS ANB TRACKS OP 



phycus^ ChloepTiycus *, Tricophycus of authors as examples of genera 

 which contain, or consist of, examples of Rill-marks. 



I may add that I have discussed other forms of such impressions 

 in my papers on Footprints of Limulus, and on the genus Rusichnites, 

 in the ' Canadian Naturalist,' and in that on " Impressions of Aquatic 

 Animals in the Carboniferous Rocks "t. In my work, 'The Geological 

 History of Plants', I have also endeavoured to state the criteria for 



Fig, 19. — Rill-marTc. Carboniferous; Nova Scotia. 



^ nat. size. 



(From a Photograph.) 



separating such markings from true Algae, and have rt-terred to in- 

 stances in which, while, on the one hand, mere markings have been 

 elevated into marine plants, on the other, true land plants, imper- 

 fectly preserved, have been degraded into Algic. I may also state 

 that in America the Clinton lormation, intervening between the 

 Medina Sandstone and the Niagara Limestone, and containing many 

 thin-bedded arenaceous and argillaceous deposits, is remarkably rich 

 in such impressions. Many of these have been figured by Prof. 

 Hall:}: and referred to worms, Crustacea, and gastropods. In the 

 vicinity of Hamilton, Ontario, large collections have been made by 

 Lt.-Col. Grant, who has enriched the Peter-Redpath Museum of 



* Miller now admits that this is not an Alga. 

 t Amer. Journ. Sci. ser. 3, vol. v. 1873, p)D. 17; 

 \ ' Paleontology of New York', vol. ii. 1852. 



&c. 



