Professor J. B. Harrison—‘ Laterite’ in British Guiana. 557 
not, in my opinion, a right to the term laterite. But I have shown 
in connexion with certain of the laterites I. have described how 
readily aluminous deposits can be formed from normal lateritic earths 
by ordinary processes of elutriation and redisposition. The accurate 
and complete account of the ‘‘ Alluviale Laterit” of Surinam by 
Du Bois is fully applicable to those of British Guiana. But personally 
Ido not apply the term laterite to these detrital deposits, which are 
equally well described as valley or river alluvia. 
I have also not described the deepest layers of the residual deposits 
which are met with in the shafts of mines below the water-table and 
closely overlying the unaltered rock. They do not, as far as my 
limited experience goes, show the characteristics to any marked 
extent of laterite either according to Buchanan’s description or to. 
more recent views. They are best described as decomposed diabase, 
gabbro, or schists as the case may be, as they largely consist of 
partially decomposed fragments of these rocks with varying amounts 
of secondary quartz, hydrates of alumina and iron, and kaolinite 
derived in part from the decomposing rocks or washed in from 
overlying lateritic earths. . 
Where the original rocks are massive and compact, are only covered 
with comparatively thin layers of lateritic products, and are practically 
above the water-table, the transition from unaltered rock to lateritic 
earth is abrupt, and few, if any, particles of the original rock, except 
grains of ilmenite and of similar highly resistant mineral, can be 
found in the residual earths lying directly in the rock. 
The Laterite of Surinam and of French Guiana.—The ferruginous 
residual earths in South America appear to have attracted the notice 
of geologists and mining experts in these countries from quite early 
periods; for example, amongst other early authors they are mentioned 
by J. B. Le Bland, Deseription de la Guyane Francaise, 1814; 
y. Eschwege, Bettrdge zur Gebirgskunde Brasiliens, 1832; Schomburgk, 
Reisen in Guyana und am Orinoko, 1841 ; Heuser, Beitrag sur Kenntnis 
des brasilianischen Kiistengebirges, 1858; Le Neve Foster, ‘‘ Caratal 
Gold-field” (Q.J.G.8., No. 99, vol. xxv, pp. 840-2); and Tate, ‘‘ Geology 
of Guyana Venezuela” (Q.J.G.S., No. 99, vol. xxv, pp. 349 and 350). 
Among more recent works in which more or less detailed accounts 
of the laterites of Surinam and French Guiana are given are: Martin, 
Reise nach Niederlindisch -Westindien, 1888; levat, Recherche et 
Pexploitation de Vor en Guyane Francaise, 1898; Du Bois, Geologisch- 
bergminnische Skizzen aus Surinam, 1901; van Cappelle, La constitution 
géeologique de la Guyane hollandaise, 1907; whilst the most complete 
account of the Surinam laterites is Du Bois’ monograph Bettrag zur 
Kenntnis der Surinamischen Laterit, 1908, to which I have several 
times referred. 
Unfortunately for the purposes of this paper the analyses given by 
the above authorities are more or less incomplete owing to the silica 
present in the form of quartz not having been determined separately 
from that present in the combined state. The analyses of ‘‘ Roche 
a& Rayvet”’ given by Levat on p. 42 of his work show that, even if 
all the silica was present in the combined state, the samples from 
Maripa would have contained 7°6 per cent. and those from Awa 
