860 



MR. H. B. MIL^s'ER ON THE 



[vol. Ixxviii, 



shows the results o£ the microscopical examination of the various 

 facies : — 





^ A 





;A 



6 



^ 6 



> i 



w, 



l^i 



Horizon A 



]M i 11 e r a 1 s . 



Quartz 



Kaolin 



Muscovite 



Glauconite 



Ferruo-iiious cement. 



Magnetite . 

 Ilmenite .... 



Garnet 



Tourmaline 

 Staurolite . 



Epidote 



Chlorite 



Biotite 



Leucoxene 

 Zircon 

 Kj^anite ... 

 Aiiatase ... 

 Eutile ... 

 l^rookite . . . 

 Topaz ...... 



Andalusite 

 Muscovite . 

 Corundum 

 Cassiterite . 

 Xenotime . 



B. 



C. 



D. 



E. 



Essential and dominant constituent througliout. 



5 5 5 5 5 6 5 



6 6 4 4 4 5 4 

 4 4 4 3 4 3 4 

 Essential autliigenous material throughout. 



A. Yellowish-hrown sand, 6 feet below the surface. Average of several samples 



taken laterally, including one from the Cornish Sand Companj-'s pit. 



B. White sand, 8 feet below the surface, Cornish Sand Companj-'s pit. 



C. Brown sand, 14 feet below the surface, Cornish Sand Company's pit. 



I). Keddish-brown sand and grit, 20 feet below the surface, Cornish Sand Com- 

 pany's pit. 



E. Chocolate moulding- sand, 22 feet below the surface, Cornish Sand Company's 



pit. 



F. Reddish-brown sand, 23 feet below the surface, bottom of the pit, Cornish 



Sand Companj^'s pit. 



G. Average composition of the St. Erth sands. 



[Conventional signs as in the previous table, p. 357.] 



A quantitative estimation of the mineralogical composition of 

 an average sample of St. Erth sand gave the following results : — 



Quartz, 91" 6 per cent. 



Authigenous and other ' light ' material, 8*26 per cent. 



Magnetic residue, 0*120 per cent. 



Non-magnetic residue, 0'025 per cent. 



