part 4] 



PLIOCEN-E DEPOSITS OF CORNWALL. 



357 



A". Peteo&eapht of the Sediments. 



(a) St. Agnes. 



The determination of the mineralogical composition of the 

 St. Agnes deposits yielded the following results : — 





Horizon 



1. 



II. ' III. IV. 





1 



Heavy Residue : Light Material ; 

 Magnetic. S.G. > 2-82. S.G. <282. 



Minerals. 

 Quartz 



Essential constituent throughout. 



— — 4 4 

 4 4 5 4 

 4 4 13 



Essential authigenous material. 



Kaolin 



Muscovite 



Glauconite 



Ferruginous cement 





Magnetite 



7 

 o 



8 

 3 

 4 

 1 



1 



7 7 ! 7 

 5 5 5 



8 8 8 

 13 3 



4—4 



2 2 2 

 2 2 2 



Ilmenite 



Garnet 



Tourmaline 



Staurolite 



Epidote 



Chlorite 



Eiotite 





(M* 



00 

 oi 



ci be 



5 



Leucoxene 



7 

 4 

 6 



2 



4 

 7 

 5 



1 



? 



7 ' 7 7 

 6 6 5 



5 16 



— 2 2 

 4,2 2 



5 5 5 



5 ' 8 7 

 5 6 5 



— ? ? 1 



— ; 1 1 1 



— : ?i ?i 



Zircon 



Kvanite 



Anatase 



Rutile 



Brookite 



Topaz 



Andalusite 



Muscovite 



Corundum 



Cassiterite 



Xenotime 





[9 = ' Flood ' of a particular species. 8= Very abundant. 7=Abundant. 

 6 = Very common, 5 = Common. 4^Scarce. 



3=Ver3^ scarce. 2 = Rare. l = Very rare.] 



I. Yellow Sand. Base of series now exposed, 15 feet below the sm-face, quarry 

 at Higher Bal. 



II. Red Sand. 12 feet below the surface, quarry at Higher Bal, 



III. * Candle Clay.' Average of several samples taken laterally, including quarries 



at Higher Bal and Beacon Cottage. 



IV. Average composition of the St, Agnes deposits. 



The residues yielded by all the members of the St, Agnes 

 deposits are characterized by the abimdance of the magnetic 

 minerals as compared with the non-magnetic, and the bulk of this 

 magnetic crop consists of tourmaline and iron-ores. In the case 

 of the red sand, the actual proportions are O'Sl per cent, magnetic 

 to 0'036 per cent, non-magnetic. The ' light ' material is mainly 



