442 Professor J. B. Harrison—‘ Laterite’ in British Guiana. 
The analyses of the soils were made in the manner usual in 
analysing them. The soils were digested in hydrochloric acid 
containing 20 per cent. of real acid at the temperature of boiling 
water for five working days, and the determinations of the constituents 
dissolved were made by well-known processes of analysis, a description 
of which it is not necessary to give here. 
Although the analyses are of value as indicating the general 
characters of the soils on the residual earths in the lateritic areas and 
as showing in some cases the presence of alumina in a state or states 
in which it is readily dissolved by hot diluted hydrochloric acid in 
higher proportions than are usually dissolved from either temperate 
or tropical soils, it is evident that they do not indicate whether the 
alumina which is soluble in hydrochloric acid is present in the form of 
hydrate or as fairly easily decomposable silicates. 
As I pointed out in a paper on the Oceanic Rocks of Barbados 
(Q.J.G.S., vol. xlvii, May, 1892, pp. 190, 191), the action of hydro- 
chloric acid in the silicates present in earths and clays is dependent 
for its extent on variations in the strength and the temperature of the 
acid and in the duration of its action. This is true also of other 
acids. It is not feasible as far as my experience goes to regulate 
these factors so that only the uncombined or hydrated alumina 
present in an earth is dissolved without any of the aluminous silicates 
being attacked and supplying some of their alumina for solution in 
the acid. Hence it is necessary in the study of the earthy decom- 
position products of rocks with the view of ascertaining the nature 
and proportions of their proximate components to analyse them by 
methods which ensure their complete decomposition, and guided by 
the indications of microscopical examination of the earths to calculate 
the proportions of their proximate constituents by means of the figures 
obtained by the analyses. 
Aided to a very great extent by Mr. K. D. Reid, an Assistant 
Analyst in the Department of Science and Agriculture of British 
Guiana, I have made in addition to earlier ones a series of more 
complete analyses by following with some additions and modifications 
the methods I described in papers dealing with the compositions of 
the oceanic rocks of Barbados and of certain oceanic oozes (Q.J.G.S., 
vol. xlviii, pp. 182-8, May, 1892; vol. li, p. 314 et seq., August, 
1895). | 
In the discussions which follow in this paper the probable proximate 
composition of the samples which have been examined have been 
calculated on the assumption that the minerals present are in the 
condition of maximum hydration corresponding to the proportions of 
water found in the samples, that the potassium, sodium, and calcium 
oxides! found therein are in the form of felspars or of sericite, 
according to the indications of microscopical and physical examinations ; 
the magnesium oxide has been calculated to tale, its most stable form 
of hydrated silicate under weathering; the portion of the combined 
silica not required in these combinations has been calculated to 
* Calcium oxide is usually found in very small proportions, and in the residual 
earths is generally present as a constituent of epidote. 
