Professor J. B. Hurrison—‘ Laterite’ in British Guiana. 
dD9 
Similar calculations based also on the assumption that the titanium 
oxide is the static constituent have been made with regard to: the 
Tumatumari, Omai Falls, and Mazaruni laterites. 
given in Table XX— 
Their results are 
TasBLe XX. 
Tumatumari. Omai Falls. Mazaruni. 
Diabase. | Laterite. | Diabase. | Laterite. Hornblende Laterite. 
Schist. 
Silica . Ba, si19 | 3043 | 53-25 | 29-90 | aio | 15°84 
Aluminium Oxide . 15°80 15°80 17°16 11°78 15°94 11°38 
Tron Protoxide . 14°28 12°53 14°40. 
Tron Peroxide ; 6°40 14°30 2°55 
Magnesium Oxide . 5°63 13 6°10 08 5°54 704 
Calcium Oxide . 9°58 14 7:46 07 9-60 “003 | 
Sodium Oxide 2°09 “08 2°50 -10 1°87 °18 
Potassium Oxide 60 <x, 69 0 | 08 16 
Water ; 30 | 6°77 30) |MieiODM AIMCO 3 
Titanium Oxide . “40 | “40 39) +39 | -30 30 | 
| | at 
99°87 | 60:27 | 100°33 63°87 99°73 33°453 
Allowing for the gain in water in each of them, for the oxidation 
of the protoxide of iron, and for a small excess of iron peroxide due 
to infiltration in the Omai Falls sample, we have losses of 47°4, 44°6, 
and 70°5 per cent. respectively of the original rocks during their 
degradation to laterite. The loss per 100 parts of each constituent of 
them is as follows :— 
TABLE XXI. 
Tumatumari. Omai Falls. Mazaruni. 
Silica . z 5 : 40°5 43°6 69°3 
Aluminium . ? : nil 31°3 28-6 
Tron Peroxide ‘ : 58°7 nil 83°6 
Magnesium Oxide oiler 9827 ~99-2 
Calcium Oxide . : 98°5 99°1 99°9 
Sodium Oxide F é 9671 96 90°4 
Potassium Oxide . , 80 47°8 nil 
The range of variation in the losses of alumina and oxide of iron is 
wide, being for alumina from m2 to 31-3 per cent. and for oxide of iron 
from nz to 83°6 per cent. 
The most interesting points in the above results are the great loss 
of combined silica and the change of some of the silica set free into 
quartz. Thus, in the Tumatumari sample 46-01 of the combined 
silica present in the rock is not found in that form in the derived 
laterite, but 25-2 of the silica set free has been changed into quartz ; 
in the Omai Falls sample 41-7 of the combined silica has disappeared, 
leaving in its place 18°2 of quartz; and in the Mazaruni sample 39-1 
of the combined silica has been apparently lost from that condition, 
whilst only 3°2 of it remains as quartz. 
