NO. 48. — 1897.] GEOLOGY AND MINERALOGY. 



51 





Felspar. 



Mica. 



Hornblende. 



Silica 



66-75 ... 



48-00 



... 4200 



Alumina 



17-50 ... 



34-25 



... 1200 



Lime 



105 ... 





... 11*00 



Potash 



12-00 



8-75 



... A trace 



Magnesia 







2-25 



Oxide of iron 



•75 ... 



•50 



•25 



Oxide of manganese 





•50 



•25 



Water 







•75 . 





98-25 



96-00 



9825 



Quartz consists of nearly pure silica, with a trace, however, of 

 alumina acid, sometimes of iron. 



None of the varieties which Kelaart classifies laterite or 

 " cabook " into, namely, (1) Laterite properly so called, and 

 distinguished as Quartzose ; (2) Lithomargic Laterite ; (3) 

 Detrital ; or (4) Laterite Gravel, is to be found in the 

 Province in any shape whatsoever. 



Clays. 



Lithomarge, which takes its place, is of frequent occur- 

 rence. According to Kelaart it is — 



A sectile clayey substance of variegated colours. It is chiefly 

 formed of a decomposed felspar and hornblende, whitish when the 

 former prevails, and yellow or reddish when hornblende predominates 

 in the rock from which it is derived, owing to the larger proportion of 

 oxide of iron which the latter mineral contains.* 



From the list of mineral constituents which enter into 

 the composition of gneiss, it will be seen that felspar and 

 mica contain the largest amount of alumina, the principal 

 ingredient in the formation of clay. In rocks in which 

 felspar and hornblande predominate the clay formed is 

 much variegated. Pure felspar forms kaolin. It is not, 

 as is popularly thought, the " kiri-meti " of the natives. 

 Kiri-meti, literally "milk clay," is a species of potters' clay, 

 and is largely used for pottery. A yellow species of it is 

 used for washing walls. On the other hand, " mahuV is the 



* Journal, C.B.R.A.S., vol. II., No. 5, pp. 210, 211. 



E 2 



