April, 1901. 81 



RECENT OBSERVATIONS 

 ON OLDHAMIA AND HISTIODERMA. 



BY PROF. GRENVIIXB A. J. COLE, M.R.I. A., F.G-S. 



The most elaborate and beautifully illustrated paper ever 

 devoted to Oldha?nia is undoubtedly that by Prof. W. J. Sollas, 

 F.R.S., published in the Quarterly Journal of the Geological 

 Society of London, volume lvi., 1900. 1 If, in summarising it, 

 I add one or two comments of my own, it is merely to show 

 that the subject is still under discussion, and that we may 

 agree with the author (p. 284) that ''the nature of Oldhamia 

 cannot yet be regarded as definitely ascertained. That it is 



of organic origin seems scarcely to admit of 



doubt ; whether the organism were animal or plant, and in 

 what manner it imprinted its traces on the rocks, are questions 

 that still await a definite solution." 



Ichnium Wattsii, described in the same paper, is " a radiate 

 system of continuous, undulating, bifurcating furrows," 

 occurring in a red shale, half a mile south of Bray Head. 

 The photograph given shows it to have a general resemblance 

 to Oldhamia radiata. Prof. Sollas compares it with Nathorst's 

 figure of the radiating impressions made by a living worm, 

 Glycera alba, and shows (p. 277) that it "does not present 

 a single feature by which it can be distinguished from the 

 track of a recent worm." 



Oldhamia, however, is not near enough to Ichnium to 

 warrant the same conclusion. The author describes, more 

 completely than has been before attempted, the two well- 

 known species from Bray, and illustrates them with photo- 

 graphs, which are fortunately printed as separate plates, and 

 which are veritable works of art. Prof. J. Joly 2 pointed out, 

 in 1886, that, on the upper surface of any bed, Oldhamia 

 radiata appears as a depression, while O. a?itiqua is in relief. 

 Prof. Sollas, with characteristic ingenuity (p. 282), explains 

 this by supposing that the upper surface of O. antiqua was 

 more resisting than the lower ; that the lower part decomposed, 



1(1 Fossils in the Oxford University Museum. III. Ichnium Wattsii, a 

 Worm-track from the Slates of Bray Head : with observations on the 

 Genus Oldhamia.''' Q.J.G.S., vol. lvi., pp. 273-286. 



2 " On a peculiarity in the nature of the impressions of Oldhamia antiqua 

 and 0. radiata." Journ. R. Geol. Soc. Ireland, vol. vii., p. 176. 



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