102 THIE INADI-t, EA iPIPE [CHAP.
moist tropical climates has given rise to the suggestion that the
alteration of the fresh rock is effected by the action of some
organism, which grows at the surface of the rock and possesses
the power of breaking up the rock silicates. The separated
silica is removed in solution, while the hydrated alumina and
iron oxide remain behind, and, by their segregative power,
cement the other products into a mass with the peculiar
structures which characterize laterite (24).
Laterite may become broken off and carried to lower levels
by the action of streams, and when re-deposited at lower levels
may become cemented again into a compact mass by the segre-
gative action of the hydrates, including sand-grains of quartz and
other minerals. Thus there are ]higkh-lz'el laterites, resting on
the rocks at whose expense they have been formed, and lozv-
level laterites, formed in the usual way of detrital deposits.
Lateritesof Laterites are not merely modern formations; several old
past ages. land surfaces show traces of lateritic deposits. On the old
surface of India, for instance, which was overwhelmed and
covered by the Deccan trap in uppermost Cretaceous times,
laterites existed, and are sometimes now exposed where the
weathering agents have cut away the protecting layer of trap.
At the base of the Tertiary rocks north-east of Surat, and at
a few other places, are rocks having such a perfect resem-
blance to modern laterite that there is little or no doubt that
the conditions for the formation of this peculiar material
existed in early eocene times, and it is probable that many of
the bauxites of Europe and America have a similar origin.
T. H. HOLLAND.
For all papers published on the geology of India before I893, references
will be found in the second edition of the official manual (Mlanual of thle Geo-
logy of India) published in that year. Results of importance which have been
obtained since, and which are noticed in this chapter, will be found more
fully discussed, with references to previous literature, in the papers named
below. In addition to these papers, certain conclusions and changes in
nomenclature are adopted in this chapter, which have not yet been made
public. These, however, have been discussed by all the officers of the
Geological Survey of India, and have been accepted as representative of
I. F. Kossmatt.-On the importance of the Cretaceons rocks in Southern
India in estimating the geographical conditions during later Cretaceous
tines. Records, Geol. Stor. Ind., vol. xxviii, p. 39 (l895). The Cretaceous
deposits of Pondicherry. Ibid., vol. xxx, p. 5r (I897).