490 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
Among places where the origin of the auriferous veins and masses 
of secondary quartz which occur in the laterite of the Guianas has been 
discussed, I may mention p. 41 of Guide Pratique pour la recherche et 
Vexploitation de Vor en Guyane Frangaise by M. EK. D. Levat (1898), 
pp- 21 and 22 of G. C. Du Bois’ above quoted work on the Surmam 
laterite (1903), pp. 11 and 12 of the Geology of the North-Western 
District of British Guiana by H. I. Perkins and myself (1897), 
pp. 208 and 209 of the Geology of the Gold-fields of British Guiana 
(1908), and pp. 28 and 29 of Goudindustrie in Suriname by 
E. Middelberg (1908). 
The attention of the technical geologists and the mining experts who 
have personally studied on the spot the residuary lateritic formations 
of the Guianas has necessarily been more attracted to the occurrence 
and nature of the secondary veins of auriferous quartz and to the gold 
disseminated in them than to the, from their poimt of view, very 
subordinate question of the presence or not of free aluminium 
hydroxide in the earths. 
Decomposed Granites, Kaolins, or Pipe-clays.—The following are 
analyses of a granite and of a hornblende granitite, and of the 
products of their decomposition by weathering in situ, and of similar 
products of a granite, and of an aplite of which the compositions are 
not known :— 
TABLE XI. 
San San 
Mazaruni. Mahdia. Kopai. 
Orealla. 
Upper | Couran- 
Mazaruni River. | Potaro River. | |Mazarunij _lyne 
River. | River. 
| Pipe-clay| Pipe-clay 
Granite. |Pipe-clay Homnblenee Pipe-clay es i dota ‘ 
5; Granitite.| Aplite. 
Quartzeee ey a he ee 36°60 38°70 29°50 88°15 
@ollordiSulicae “Spe 1:60 “43 
Combined Silica. . Blea 27°68 38°70 25°24 
Aluminium Oxide . 13°98 19°82 15:83 | 24°60 
Tron Peroxide 0:93 2°05 2°86 2°67 
Tron Protoxide . . 0°46 0°51 
Magnesium Oxide . 0:72 itil 2°14 “39 
Calcium Oxide . 0°88 nil 3°49 “10 
Sodium Oxide 2:80 39 3°07 nil 
Potassium Oxide 4°81 50 2°88 “41 
Water 2 0°74 8°52 0°50 6°92 
Titanium Oxide. . . 0°62 | *85 0°46 1°01 
Phosphoric Anhydride . 0°06 “01 0:01 nil 
Manganese Oxide 0:24 | trace 0°08 nil 
100 | 100°28 100:03 | 99:93 
Their mineralogical compositions are shown as follows :— 
