272 MK. E. AVETHEKED OX THE OCCUERENCE OF 



This analysis shows that the amount of magnesia present is less 

 than in the previous analysis. This is accounted for by numerous 

 minute veins of calcite which traverse the rock. These are clearly 

 of secondary origin, and in an analysis would, of course, increase 

 the percentage of carbonate of lime. The oolitic spherules are 

 very similar to those which I have described from the base of the 

 middle series. They average about -52 millim., and are therefore 

 slightly smaller than those previously described. No sign of Gir- 

 vanella was discovered in these beds. 



4. The next limestone which shows oolitic structure occurs a 

 short distance below where the New E-oad from Clifton joins the 

 road along the banks of the E-iver Avon, and for convenience I will 

 call it the "New-Eoad Oolite.'' The beds differ from those pre- 

 viously noticed ; they do not rest on dolomitized limestone, and are 

 not so crystalline. The following section shows the character of the 

 beds : — 



Section of the New-Road Oolite. 



ft. in. 



1. OoHtic limestone, with corals at the top 10 



2. Dark nodular limestone with argillaceous material 9 



3. Blue limestone with some oolitic spherules 2 6 



4. Oolitic limestone 3 6 



5. Grey limestone ; oolitic in part 2 8 



6. Base, Coralline Limestone. 



Commencing an examination from the top, the sections were 

 made from specimens collected throughout the 10 feet of rock. The 

 oolitic spherules are slightly ferruginous, and some of them are as 

 large as 1 millim. in diameter, and the average may be put at about 

 •8 millim. In some the nucleus is well preserved and consists of a 

 Poraminifer, a joint of a Crinoid, a portion of a spine, or a fragment 

 of shell. The nucleus is surrounded by a concentric arrangement, 

 but the crystalline radiate feature is only slightly developed in a 

 few instances. 



A form of Girvanella was here discovered to which I propose to 

 give the name of Girvcmella Ducii, for reasons to be presently ex- 

 plained. It consists of an aggregation of tubules similar to those 

 represented in PI. XI. figs. 2 a and b ; but in this instance the out- 

 lines are to a large extent obliterated by mineral changes ; the centre 

 of the granule has been converted into calcite, and the concentric 

 arrangement now presents a dark granular crystalline structure. 

 Throughout the whole of this the tubules of Girvanella Ducii can 

 be seen. The concentric arrangement is similar to that of the 

 other granules or spherules in the slide, and I have given it very 

 careful examination with the object of determining whether it 

 is of organic or of inorganic origin. Seeing it for the first time, an 

 observer would be disposed to pronounce in favour of the latter view : 

 but after the study I have made of the structure of oolitic spherules 

 I am disposed to regard it as organic. The apparent concentric 

 layers may be a series of tubuli, the outlines of which have become 

 obliterated by mineralization. That some of the spherules in the 



