2/8 MK. E. WETHEREI) ON THE OCCUREENCE OF 



the structure can be easily made out. It is probably owing to the 

 fact that slides are generally covered with balsam that the structures 

 I am about to describe have not before beeu detected. I have 

 myself rendered many of my slides almost useless by reason of the 

 high refractive power of Canada balsam. 



The best examples of oolitic structure are to be found in the 

 " Osmington Oolite " of Blake and Hudleston* ; but there may be 

 said to be several types of oolitic spherules in the Coralline Oolite. 

 I. A spherule with a minute loosely aggregated form of Girvanella 

 tubules as a nucleus, which are surrounded b}' an irregular sort of 

 concentric arrangement (PI. XI. fig. 6 a). 2. The same form of minute 

 Girvanella occurs in loose aggregations or surrounding foreign 

 objects (fig. 6 h) ; in these instances forming granules or spherules. 



3. A spherule or granule made up of a mass of loosely-aggregated 

 very vermiform tubuli which are larger than the last (fig. 7). 



4. A spherule or granule in which the nucleus generally consists 

 simply of calcite, and the concentric arrangement has a granular 

 crystalline appearance, in which occasional outlines of tubuli may 

 be seen. In short, we get in these spherules the same appearance 

 that we see in those obtained from the Upper freestones and 

 Clypeus-Plottii beds of the Inferior Oolite, which I have represented 

 in fig. 4. 5. A spherule with a clear and well-defined concentric 

 arrangement around a nucleus (fig. 8). 



With regard to the first of the above spherules or granules, in 

 which the Girvanella-tuhwle^ occur in the centre (fig. 6 a), I regard 

 the tubes simply as the nucleus, and the concentric structure as 

 foreign to the nucleus. That this is so, is proved by the fact that 

 Girva}iella-i\ih\A(i^ of the same form are met with apart from the 

 concentric arrangement (fig. 6, 6). It is then a question whether 

 the concentric structure is of concretionary origin or a form of 

 Girvanella. A casual observer would probably either give no 

 opinion at all, or decide in favour of the concretionary origin. 

 A careful examination, however, of other spherules in the slides 

 shows that they exhibit the same structure ; and in some there 

 are unmistakable outlines of tubules. I am therefore obliged to 

 come to the conclusion that the structure is organic, and the same 

 may be said of other spherules in the slides which show similar 

 structure. 



With regard to the class of spherules which I have mentioned 

 under the head of 3, they are simply an aggregation of a species of 

 Girvanella, which I propose to call G. intermedia. Spherules of this 

 type are fairly numerous in the bed of Coralline Oolite from which 

 the slides were taken, and which occurs on the sea-shore at AVyke, 

 near Weymouth. I have not found the tests of this species attached 

 to foreign objects. 



S])herulcs of the type represented by fig. 8, are quite different from 

 those before described. They are more truly ciystalline, and the 

 granular crystalline feature is absent. Also the structure around 



* Quart. Journ. Geol. Soc. vol. xxxiii. p. 205. 



