502 Miss C/inpniaii — Carhoniferous Limestone, Avon Gorge. 



Productus cora, mut. S3 subzone. 

 Seminula Oolite. 



Total . 



100-16 



As is usual in the Oolitic limestones there is very little impurity. 

 The Mg cannot be seen as dolomite rhombs in thin sections of the 

 rock even when treated with Lemberg's solution, and can only be 

 detected on analysis. 



The insoluble residue consists of fine argillaceous material, quartz 

 with secondary growth, zircons, pyrites, and well-developed siliceous 

 sponge spicules. No carbonaceous material is present. 



No coral bands occur, so the small amount of insoluble residue cannot 



be due to the formation of these beds under coral-reef conditions. 

 I 



' D. DiBUNOPHYLLUM ZONE. 



Total . . 100-10 100-18 100-26 



The insoluble residue is mainly rounded detrital silica and quartz 

 flakes. Much carbonaceous material occurs at tlie top, bitumen in 

 one case constituting 4-16 per cent of the entire rock. 



Lonsdalia floriformis subzone. 



D2 



Ca 



MgO 



C O2 



Fe2 03 + AI2O,, 



Insoluble residue 



54-96 



43-41 



-66 



1-84 



Total . . 100-87 



The content of insoluble material varies between -02 and 

 2-41 per cent — it is chiefly quartz and fine argillaceous material. 

 The Dibunophyllum zone contains many marked coral bands, and 

 was probably deposited under " coral-reef conditions". It contains 

 a very variable amount of insoluble residue up to as much as 

 43-29 per cent. 



On examining the foregoing results it will be seen that the beds 

 whicli have been formed under coral-reef conditions have a very 

 variable amount of insoluble residue. 



In the rocks analysed it varies between -43 in Zo and 43-29 in D^. 

 On the other hand, rocks which do not appear to liave been formed 

 under coral-reef conditions, e.g. Ko, are remarkably pure. On the 



