Professor J. B. Harrison—‘ Laterite’ in British Guiana, 559 
reminded me of Logan’s account of the ferruginous and silico-ferru- 
ginous rocks and laterite of Singapore (Q.J.G.S., vol. yi, p. 331, 1851), 
and of Mr. Scrivenor’s description of the laterite of the Malay 
Peninsula (Grotocicat Macazinr, September, 1909, No. 543, p. 431). 
The view that I have formed after many years’ fairly intimate 
acquaintance with the Guiana residual deposits in the field and in the 
laboratory is that the terms laterite or lateritic earths are both useful 
and convenient ones to denote the whole mass of the residual deposits 
which are characterized by the occurrence in them of concretionary 
masses varying from highly ferruginous to highly aluminous, as well 
as, in places, by the presence of secondary silica in quantity. In 
my opinion laterite of the above nature can be accurately defined, 
following Du Bois (p. 3 of his monograph), as the weathering 
product of igneous or metamorphosed rocks in which by chemical 
decomposition the silicates contained in them have been changed to 
secondary siliceous compounds, secondary silica and alumina, and to 
oxides of iron in more or less hydrated forms. Following Mr. Scrivenor 
the laterite can be conveniently classed into siliceous, ferruginous, or 
aluminous laterite as its composition indicates, whilst the highly 
aluminous masses present in them can, in my opinion, be best and 
most accurately described as bauxite. The above definition would 
cover not only the aluminous masses to which it has recently been 
proposed to restrict the term laterite, but also the great majority of 
these which possess, in parts at any rate, that property of setting 
from which the name was originally derived. It would also cover the 
residual lateritic deposits of varying compositions, due to climatic and 
other conditions, found in different parts of the Indies. 
It is not possible in the Guianas to ascribe the production of 
lateritic deposits to regular alternation of dry and wet seasons. 
Du Bois gives a table in his work from which I have calculated 
in inches the average monthly rainfall in Paramaribo, Surinam, for 
the years 1896 to 1901. This and the average monthly rainfalls 
during sixteen years at stations in British Guiana situated on laterite 
are shown in the following :— 
TABLE XXV. 
Surinam. British Guiana. 
Paramaribo. Mean of 10 inland 
1896-1901. stations on I.aterite. 
1891-1906. 
Inches of rain. Inches of rain. 
January. : : : 5°24 7°06 
February. : : : 5°61 4-29 
March P F : ; 8:65 7°22 
April . 5 : : : 8 39 8 
Nia? See eco ae aie ea 12-25 11:89 
June . ; : 4 - 11°65 12°45 
July . : > : é 6°37 10°69 
August . : ‘ - 5°49 7°96 
September . ‘ ; . 2°66 5°22 
October i 4 : : 3°45 4:93 
November . : : : 7 6°57 
December . 3 : 5°49 10 
82°25 95°58 
