66 
Records of Ike Geological Survey of India. 
[vol. xi. 
resembles those of younger volcanic formations. The elevatory power has, however acted 
most strongly on the southern islands, and has here upheaved sandstones and slates probably 
to heights of 1,500 to 2,000 feet above the level of the sea; on the low northern islands 
the same power was, on the contrary, weakest. 
With regard to the sedimentary deposits, I may state that Rink called (he argillaceous 
deposits of the northern islands “ older alluvium,” and the sandstones and slates of the 
southern islands ‘'brown-coal formation.” In separating them from each other, he considers 
the former as being derived from plntonie rocks through chemical and mechanical decom¬ 
position, and as only of a local character. According to this the archipelago of the Nieobars 
is divided by him into two geologically different groups,—an opinion with which I cannot 
agree. 
The clays and clay-marl formations of the northern islands, Car-Nicobar, Teressa, 
Bompoka, Camorta, Trinkut. Nancowry, and the sandstones and slates of the southern 
islands, Katohall, Little and Great Nicobar, appear to be only petrographically different 
products of one and the same period of deposition. There are at the same time very few 
materials from which the age of the marine formations could be determined, as the only fossil 
remains which have been found in their strata are fragments of drift wood changed to brown 
coal, plant impressions resembling Fucoids, Foraminiferu and Polyeistince. But all these 
remains indicate more or less distinctly a young tertiary age. 
The same conclusions are derived from a comparison with the geological conditions of 
those islands which lie on the same line of elevation as the Nieobars; I refer especially to 
Sumatra and Java. 
I have not the least doubt that the clay-marl and sandstone formation has its perfect 
analogue among the tertiary deposits of Java, which I had myself the opportunity of studying 
and comparing in their distribution and lithological character. These became first known 
through the late Fr. Junghubn, whose researches on the physical geography of Java are 
of such merit. 
According to Junghubn, one-fifth of the surface ground of Ja va is alluvial soil. This 
is especially prevalent on the northern side of the island, extending from the coast inwards 
either one, or sometimes five to ten English miles ; one-fifth of the island consists of volcanic 
cones, ami their immediate vicinity where the lower l-oeks are covered lip by volcanic products. 
These conical hills chiefly occupy the interior of the island, sometimes in a double range 
stretching from west to east; while three-fifths of the area are occupied by tertiary rocks. 
Either in flat protuberances or in clod-like elevations, these tertiary rocks surround the 
volcanic range always on two sides, on the southern as well as on the northern. On the 
northern side, the less highly upheaved tertiary strata underlie the alluvium, and therefore 
occupy on the surface a small area. In an unequally greater degree, the lertiary deposits are 
developed on the southern side of the volcano, both as regards height and horizontal 
extent. They are mostly visible split in clods (sehollen) which always rise higher towards 
one side,—the north, or towards the volcanoes,—and arc at their highest edge upheaved to 2, 
3 and even to 4 thousand feet. It is also principally on the southern side that platonic rocks 
occur in the neptniiinn deposits of Java, which are occasionally only represented by narrow 
and sharply defined veins, without any influence upon the structure and configuration of the 
surface; sometimes, however, they form small bill ranges or isolated bills, similar to the 
serpentines and gabbros of the Nicobar islands. 
According to the reports of the Dutch Mining Engineer, Iliigneniu,* a repetition of 
the geological formations of the Nieobars appears to be met with in the Tjilut.uk Bay (the 
southern lateral bay of the Wynkoop Bay on the southern coast of Java). The prevalent 
formations hero are sandstone-conglomerate and highly developed green stone-breccias, besides 
plntonie rocks of the greenstone group. From specimens which I had an opportunity of 
seeing in the local collection at Boutenzorg, I found that these plutouic rocks are serpentines, 
gabbros and aphanites, exactly similar to those of the Nieobars. Equally identical appears 
to be the chalk-white clay-marl in the middle portion of Bantan, and the fine white marls 
in the southern portion of Tjidamar, mentioned by Junghubn (loc. cit., p. 13), with those 
occurring on the Nicobar islands. 
* Naturkundigc Tijdselmft voor Ncderliuutiscll Indie, Tkeil XIX, p. 110, 1850. 
