586 MESSES. JUKES- BROWNE AND W. HILL ON THE LOWER, PART 



following is an analysis made by Mr. W. D. Severn of the marl 

 found at a depth of 5 feet in our boring at Eoydon : — ■ 



Residue insoluble in HC1 25*55 



Carbonate of lime 66*31 



Alumina 3*33 



Iron (as Pe 2 0 3 ) -81 



Magnesia *46 



Phosphoric acid trace. 



Moisture (at 100° C.) 1-85 



98-31 



The percentage of carbonate of lime in this sample is, undoubtedly, 

 a very high one, and the marl is evidently far more calcareous than 

 the Upper-Gault Marl of Folkestone, in which Mr. Hudleston found 

 only 25 per cent. But it is obviously more logical to compare the 

 Norfolk Marl with the Upper Gault of some more northern locality 

 than Polkestone ; and we have already mentioned the calcareous 

 aspect of the Upper Gault of Bedfordshire, some of which has also 

 been mistaken for Chalk-marl. We are indebted to Mr. Severn for 

 the following analysis of a sample from Pancourt brickyard : — 



Pesidue insol. in HC1, silica and silicates 38*21 



Carbonate of lime 53*50 



Alumina 3*90 



Iron(asPeO) 2*00 



Phosphoric acid *09 



Moisture (at 100° C.) 2*00 



99*70 



It will be seen that this marl contains twice as much carbonate of . 

 lime as that of Polkestone, and, consequently, that the proportion 

 comes very much nearer to that in the Poydon marl — an approxi- 

 mation which strengthens the conclusion already arrived at, that the 

 Norfolk marl is an actual northward continuation of the Bedford marl. 



The following (A) is an analysis of the limestone which lies at 

 the base of this marl in the Poydon cutting ; it was made for us by 

 Dr. W, Johnstone, and we have placed beside it an analysis by 

 Prof. Way, of a hard bed in the Chalk-marl of Parnham (B), which 



has a very similar composition : — 



A. B. 



Insoluble residue (silicates, &c.) . . 6*64 7*26 



Carbonate of lime 89*46 85*95 



Sulphate of lime 1*32 -10 



Carbonate of magnesia '18 1*18 



Potash and soda — 1*47 



Manganese '40 — 



Alumina 1*40 -20 



Peroxide of iron 1*10 1*74 



Soluble silica — 2*11 



100*50 100*01 



/ 



