904 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
has taken place. To ascertain this it is necessary to re-calculate the 
analytical figures so that their proportions are comparable to those of 
one of the constituents which is assumed to have remained unchanged. 
The structures of the Surinam and the British Guiana bauxitic laterite 
show clearly that, contrary to what is not unfrequently assumed, 
alumina cannot be regarded as a static component in rocks and their 
decomposition-products. It is evidently under condition of lateritiza- 
tion capable of entering into solution, transference from place to place, 
and redeposition in the form of alumina hydrate where conditions are 
favourable. The constituent which appears to be the most stable 
under conditions of weathering is titanium oxide, especially that 
present as ilmenite. But unfortunately as a rule it is present in such 
low proportions in rocks and in their residuary products that, when 
taken as the static constituent, errors in analysis of low value are 
productive of variations of wide extent in the results calculated 
on them. | 
When calculations of this sort are made on the epidiorite of Issorora 
and on the lateritic earth with its enclosed pisolites the difficulty 
arises that the iron in the earth and in its enclosed pisolites has not 
been derived only from the portion of the rock which has given rise 
to the earth, but is largely an infiltration product from other lateritic 
earth which has been removed by denudation. 
The results calculated on titanium oxide as the static constituent 
are as follows :— 
Taste XVIII. 
Original Karth with 
Epidiorite. Pisolites. 
Silica . r . : ; : 49°06 (Pill 
Aluminium Oxide . : F ; 18°87 10°69 
Iron Protoxide . é 5 ; 6°38 
Tron Peroxide ; : : ; 21-26 
Magnesium Oxide . : 0 : 10°95 21 
Calcium Oxide . 3 A é 11:70 oil i 
Sodium Oxide ‘ ; i ‘ ‘97 “02 
Potassium Oxide . : ; ‘ “06 “09 
Water . ; 3 : : : 43 3°66 
Titanium Oxide . : : ; “88 “88 
Manganese Oxide . ; ; < 34 01 
99-64. 44-44 
The excess of iron, the increased amount of water, and the gain 
in weight of the oxidation of the protoxide of iron in the original 
rock being eliminated, it is seen that of 100 parts of the constituents 
of the epidiorite only 26:4 remain in the laterite and that therefore 
a loss of 73°6 per cent. of the epidiorite has taken place. This loss 
falls on its constituents in the following proportion shown as losses 
per 100 parts of each :-— 
TABLE XIX. 
Silica . : : ‘ : : 84°7 
Aluminium . 2 - ‘ é 43°4 
Magnesium Oxide . 5 : : 98-1 
Calcium Oxide , : f 5 99-1 
Sodium Oxide : : E Z 97:9 
Manganese . 3 ; : 97 
os 
