560 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
In the dense forests of the Guianas there may be said to be 
a perpetual wet season, as under the shade of the trees even during 
periods of comparative drought the land is invariably wet and more or 
less soaked with water containing organic acids in solution. 
The only factor indicated in the Guianas as governing the production 
of lateritic deposits as opposed to that of pipe-clays is the original 
composition of the rocks. Rock in which plagioclase felspars with 
their usual concomitants of ferro-magnesian minerals are abundant, 
give rise by their decomposition in situ to laterite; those in which 
alkali felspars are predominant as a rule decompose to pipe-clays or 
kaolins. 
The protective influence on the soils of the very heavy tropical 
forests which in the Guianas specially characterize the areas of 
lateritic residual deposits is very great. When the land is cleared 
of forest denudation rapidly removes the fine constituents of the 
earths, leaving on the surface the masses of ironstone, bauxite, and 
quartz. The Christianburg-Akyma deposits show that under conditions 
of which we have no indication a lateritic decomposition-product may 
differentiate into angular secondary quartz-sand and into concretions 
and impregnations of secondary hydrates of aluminium and iron. 
It has been repeatedly stated that the production of laterite is 
confined to countries having hot, moist climates. Positive evidence 
as to this appears to me to be wanting. That the preservation of 
lateritic deposits is largely confined to more or less tropical countries 
I willingly admit, as it is the absence of frost that allows of the 
accumulation of deep deposits of laterite. The property of hardening 
or setting when exposed to the atmosphere which these deposits 
exhibit in parts, although sufficient for their protection under tropical 
conditions, would be of little effect were the deposits exposed to 
frost. Under temperate conditions the accumulation of laterite in 
situ to great depths would be more or less impossible ; the residuary 
matters would be subject to rapid detrition and denudation, their 
hardening properties would not be developed or only to a slight 
extent, and what under tropical conditions would form laterite would 
be redeposited as alluvial detritus, in which the presence of free 
hydrate of alumina would not be easily recognized. 
The majority of the analyses which have been made of such 
alkaline deposits have been for agricultural purposes, and in such 
analyses, unless the attack of the dilute acid used is continued for 
a great length of time, a considerable proportion of the alumina, 
which is in the form of hydrate, which is resistant to a marked degree 
to the action of weak acids, will not enter into solution and will be 
included amongst the sand and insoluble silicates. It is therefore 
possible that the proportions of alumina present as hydrate have been 
underrated in many analyses of the clays and earths of temperate 
countries, and that if analyses were carried out on lines adapted for 
the determination of the proportion of silica present as quartz, or 
colloid silica, and in the combined state and of the total amounts 
of alumina and other bases present, earths with noticeable proportions 
of other hydrates of alumina would be found not to be of rare 
occurrence. In connexion with the possible presence of alumina 
