OOLITE OF TIlC COTTKSWOLl) HILLS. 5G7 



On tlie whole the proportions of residue shown in the above tablo 

 are low ; the exceptions are Nos. XIV., XI 1 1., VIII., and VI. Of 

 these, No. VIII. is from an argillaceous bed, and would naturally 

 give a high i)roportional residue. 



The following tables give the percentages of residue in the Lower 

 Freestone : — 



Percentage of Average size 

 Insoluble of Quartz- 



Residue, grains in mm. 



Leckhampton, No. 3 11 Oil 



„ 2 0-9 0-14 



„ 1 0-8 013 



Polyzoa Bed, Cleeve 30 0'22 



Coral Bed, Crickley 3-2 0-06 



Excluding the Polyzoa and Coral Beds, the Freestones show a 

 remarkably low percentage of residue. No. 3, Leckhampton, was 

 taken from near the top of the Freestones, not far below the Oolite 

 Marl. It will be noticed that there is an increase in the proportion 

 of residue in that estimation, and a decrease in the size of the 

 ^]uartz-grains, thus indicating the coming in of the Oolite Marl. 



The following table gives the percentage of residue in the Oolito 

 Marl : — 



Percentage of Average size 

 Insoluble of Quartz- 



Residue, grains in mm. 



From the top 3'5 010 



From the middle 31 008 



From the bottom 32 0-09 



The term " marl " would lead us to expect larger residues than are 

 shown in the above table, and in order to test the correctness of the 

 estimations, and also to ascertain whether the marl contains much 

 free alumina, I made an analysis which gave the following result : — 



Analysis of the Oolite Marl at Lechhampton. 



Dried at 212° F. 



Insoluble residue 3*1 



Alumina, with trace of iron 1 '7 



Carbonate of lime 94'4 



Carbonate of magnesia 0-5 



Alkalies, by loss 0'3 



1000 



The above analysis proves the correctness of the residue estimations. 

 It shows also that there is very little free alumina present in the 

 marl, and that 94*4 per cent, of the whole is calcium carbonate- 

 The 3*1 per cent, of residue is chiefly silicate of alumina ; it there-- 

 fore appears that this small quantity is sufficient to give a marly 

 character to the strata. 



