V.—The Residual Earths of British Guiana commonly termed ‘Laterite’

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Abstract
The losses of their constituents during the decompositions of the rocks.— As shown in this paper the analyses of the rocks and of their decomposition-products do not indicate the extent of the degradation which has taken place. To ascertain this it is necessary to re-calculate the analytical figures so that their proportions are comparable to those of one of the constituents which is assumed to have remained unchanged. The structures of the Surinam and the British Gruiana bauxitic laterite show clearly that, contrary to what is not unfrequently assumed, alumina cannot be regarded as a static component in rocks and their decomposition-products. It is evidently under condition of lateritization capable of entering into solution, transference from place to place, and redeposition in the form of alumina hydrate where conditions are favourable. The constituent which appears to be the most stable under conditions of weathering is titanium oxide, especially that present as ilmenite. But unfortunately as a rule it is present in such low proportions in rocks and in their residuary products that, when taken as the static constituent, errors in analysis of low value are productive of variations of wide extent in the results calculated on them.

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