PROCEEDINGS OF THE COTTHSWOLD CLUB 37 



In this the Professor argued that the ooHtic texture 

 might originate in many ways, and (h-ew attention to the 

 close resemblance of the internodal grains of nullipores 

 to grains of oolite. I was also at work on the same 

 subject, and in 1889 I wrote a paper ''On the Microscopic 

 Structure of the Jurassic Pisolite,""^' in which I proved 

 that these larger forms of oolitic granules were not 

 concretions, but were formed by an incrusting process 

 produced by the genus Girvanella. In fact these larger 

 oolitic granules called "Pisolites" or "Pea Grit" are 

 simply the work of incrusting organisms on a large scale. 



More recent observationsf have convinced me that all 

 oolitic granules, large and small, are of organic origin. 

 Figs. 4A, the majority being the work of a variety of 

 incrusting organisms, but others apparently, originating 

 from growth not necessarily around a nucleus. The 

 process is illustrated in Fig. 4A, where it will be observed 

 that the calcareous fragments which settled on the floor 

 of the sea are coated with a crust, some being entirely 

 enclosed and appear in the fossil state as " oolitic granules." 

 In this way freestones have originated. 



As to the nature of the incrusting and oolite-forming 

 organisms, it is possible that they may belong to the 

 calcareous algae. As I have said it is to this low order 

 of vegetation that Rothplatz assigns the oolite granules in 

 the Red Sea and Great Salt Lake. If the fossil ones 

 have a similar origin, then there is again further proof of 

 the teaching of Hutton that the past is to be explained by 

 the present. 



* Gcol. Mag., N.S., Dee. iii, vol vi, pp. iq6-200, 1887. 



t Forni.ation of Oolite, Qu.irt. Joiirn. Geol. Soc, vol. li, pp. 196 205, 1895. 



