274 :VIR. E. WETHERED ON THE OCCURRENCE OP 



Insoluble residue 3-10 



Organic matter 3*60 



Magnesia 12-10 



Lime 42*25 



Carbonic acid 38*80 



Oxide of iron and alumina trace. 



Alkalies, &c , -15 



100-00 



I have also found a good specimen of Girvanella Ducii (fig. 2 c) in 

 oolitic limestone at Tortworth Park, Gloucestershire, the residence 

 of the Right Hon. the Earl of Ducie. The horizon corresponds 

 with the Clifton oolite at the base of the Middle Limestones ; but 

 at Tortworth the beds are not so crystalline. As to whether or 

 not the beds rest on dolomitized limestone could not be ascertained, 

 as the strata at the base were not exposed. This specimen of 

 G. Ducii was the first I discovered in Carboniferous rocks, and I 

 dedicate the species to his Lordship. 



In this specimen the central tubuli are surrounded by a radiate 

 and in part concentric arrangement, which also characterizes some 

 of the other spherules in the rock ; and in this there are the out- 

 lines of undoubted tubes, which seem to point to the structure being 

 of organic origin. 



So far, then, I have discovered two species of the genus Oirvanella 

 in the Carboniferous Limestone, and these only in rocks of oolitic 

 structure. 



It may at first appear strange that Girvanella has not been 

 discovered in oolite resting on dolomitized limestone, and a 

 connexion, between the latter and the oolite may be suggested. I 

 was at first disposed to believe that this was so, but the absence of 

 dolomitized limestone at the base of the New-Road Oolite dispelled 

 that idea. It is, however, noticeable that in the Forest of Dean 

 there is a thick series of oolitic beds, and tliese also rest on dolo- 

 mitized limestone. The only connexion between the two types of 

 rock appear to me to be that both are highly crystalline ; and it may 

 be due to this fact that we find no reliable signs of Girvanella in 

 the oolites which rest on dolomitized beds, the structure having been 

 obliterated in the process of crystallization. 



The Jurassic Oolites. 



All the specimens I have examined from the Jurassic rocks were 

 collected in Gloucestershire or in the neighbourhood of Bath. 



Commencing at the base of the Inferior Oolite in the northern 

 Cotteswold area, we find coarse oolites of the Pisolitic type, which 

 series are finally brought to a close by the fine development of large 

 spherules known as the " Pea-Grit." These, as I have already 

 stated, are not concretions but the organism I have named Girvanella 

 pisolitica *. 



* See my paper in the Geol. Mag. dec. iii. vol. vi. (1889), pp. 190-200, 

 plate vi. figs. 8-11. 



