42 CONTRIBUTIONS TO THE ORNITHOLOGY OF INDIA. 



the description of the earthquake seems trustworthy, as I had 

 myself occasion to observe on Kondul the mountain-slips referred 

 to in the account. 



" These few observations, combined with those of Dr. Rink, give 

 us the following, probably still very imperfect, idea of the geolo- 

 gical nature of the Nicobar Islands : — 



" Among the various geological formations on the Nicobar Islands, 

 three are the most important : — 1 — An eruptive serpentine and gabbro 

 formation ; 2 — Marine deposits, probably of a later tertiary aye, 

 consisting of sandstone, slates, clay marls and plastic clay ; 3 — 

 Mecent coral reef formations. 



"The serpentine aud gabbro formations of the Nicobars is 

 characteristically of an eruptive nature. The tertiary sandstones, 

 slates and clay-marls appear forcibly broken through ; their strata 

 are partly inclined, partly bent in flat, parallel, wave-like undula- 

 tions. These rocks are accompanied by coarser and finer breccias 

 composed of angular fragments of these same rocks, and they 

 can partly be regarded as friction-breccias, partly as sedimentary 

 tufas in which beds of an argillaceous marl are interstratified. 

 The eruption of these plutonic masses appears, therefore, to belong 

 to a time when the formation of the marine deposits was partly 

 completed, partly still in progress. They broke through on lines 

 of fracture of which the principal strike from S. S. B. to N. IS". W. 

 agrees with the longitudinal extension of the islands. On the 

 middle islands, the serpentine and gabbro attain their greatest 

 development ; on Tillangcbong, Teressa, Bompoka, Camorta and 

 Nancowry they form bare hill-ranges of from 2,500 feet elevation, 

 and their configuration often marvellously resembles those of 

 later volcanic formations. The elevatory force 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 that force 

 was, on the contrary, weakest. 



" 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, Katchall, 

 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, Foraminifera and Polycistince. But all these remains 

 indicate more or less distinctly a late 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 Nicobars ; 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 



