12 SCIENCE PROGRESS. 



The author of a recent paper on oolitic structure con- 

 cludes with the following words : " In concluding this paper 

 I should like to say, first, that it has been my object to pro- 

 duce evidence that oolitic structure is not always of con- 

 cretionary origin. That it is all organic I am not prepared 

 to maintain, but it may be." 1 The change of view thus 

 expressed by Wethered is the outcome of a more intimate 

 acquaintance with the minute structure of oolitic grains. 

 In sections of oolitic rocks from various Palaeozoic and Meso- 

 zoic horizons it has been conclusively demonstrated that a 

 small tubular structure is of very frequent occurrence in 

 the individual calcareous grains. To this tubular fossil has 

 been assigned the name Girvanella. The name was chosen 

 from the discovery of this structure in Ordovician rocks in 

 the Girvan district of Scotland. Nicholson and Etheridge 

 have given the following diagnosis of the genus : " Micro- 

 scopic tubuli, with arenaceous or calcareous (?) walls, 

 flexuous or contorted, circular in section, forming loosely 

 compacted masses. The tubes, apparently simple cylinders, 

 without perforations in their sides, and destitute of in- 

 ternal partitions or other structures of a similar kind." 2 

 Without expressing themselves very decidedly as to 

 the systematic position of the genus the authors are 

 inclined to regard it as a rhizopod. Since its dis- 

 covery in the Girvan rocks Girvanella has been re- 

 peatedly found by other observers in strata of different 

 ages. The careful researches of Wethered have been 

 especially important in drawing attention to the widespread 

 occurrence of this problematical organism. Possibly it may 

 eventually find a definite place among fossil algae, but at 

 present it is safer merely to suggest such a systematic posi- 

 tion rather than to attempt a more precise determination. 

 The discovery of this new structure in oolitic grains has 

 naturally called forth numerous and diverse expressions of 

 opinion as to its probable nature, but it is unnecessary to 

 attempt a detailed examination of such speculations. 



In an interesting contribution from Prof. Nicholson, 



1 Wethered (2), p. 281. 2 Nicholson and Etheridge, p. 23. 



