PART 4.] 
Foote: Geology of North Arcot District. 
205 
son, c. E., Cliief Engineer of tlie Madras Railway, wlien Resident Engineer at 
that place. 
There can be little doubt that the great accumulations of well rolled quart- 
Age of certain shingle zite shingle which rest on the southern bank of the 
beds. Nagari Nose mountain and on the flanks of some of the 
mountains fui-ther north must, in part at least, be reckoned as of the age of the 
lateritic period, as they correspond closely in position and mineral character with 
the higher-lying lateritic beds just mentioned. The Nagari Nose shingle bed 
is deeply stained with iron from the ferruginous mati'is which must have once 
surrounded the perfectly non-ferruginous quartzite shingle, for that is the only 
way of accounting for the deep and indelible purple-red color borne by the 
natural pale-colored quartzite. As now seen, the shingle suggests instantly 
the idea of its being an old raised beach. 
The origin of the lateritic formations, owing to the total absence of all 
organic remains (the chipped implements being only indirectly of organic 
origin), is wrapped in obscurity and doubt. Three theories have been pro¬ 
pounded to explain the existence of these formations which fringe the western 
and eastern sides of the peninsula from a little south of Bombay right round to 
Cuttack and still further north. The three theories have been discussed at 
some length, each having something in its favor, but they are still subjudicef 
and this is not the place for continuing the discussion.‘ 
They may be briefly designated as the marine, the fluviatile, and the sub¬ 
aerial. As at present seen, none is altogether sufficient to explain the various 
difficulties, and it is very possible that all three must be enlisted before more 
light can be thrown on the subject. 
The Alluvial Eoemations. 
The alluvia occurring within the North Arcot district are all of fluviatile 
origin, and occupy the valleys of the principal rivers, but are developed only to a 
very moderate extent, and would offer no points of special interest were it not 
that in two cases there is evidence of the rivers having changed their courses 
widely and formed a second series of deposits in other valleys. 
The first of these cases is that of the Palar, the principal river of the district. 
Change of course of which now flowsintotheseaforty-twomilessouthof Madras, 
the Palar. but which formerly flowed down what is now reckoned 
the alluvial valley of the Kortelliar river and entered the sea somewhere to the 
north of Madras, probably between Gunore and Pulicat. A glance at the 
geological map will show that the present valley of the Palar is very dispropor¬ 
tionate in size to the river, and equally that the alluvium of the Rortelliar is 
gi’catly disproportionate to its river, which now flows in a deep channel. 
■ For the discussion of these theories, the reader is referred to Mr. Foote’s papers on tlie subject 
of stone implements in Southern India in the Madras Literary .lourual for October 1866, the 
Quarterly Journal Geological Society of 1868, l). 48t, and the Memoirs Geological Survey of India, 
A^ol. X, pp. 51, &o. Also stone Implements of Great Britain by John Kvans, n.c.L., F.E.S., and lastly, 
to the resume hy Mr. W. T. Blanford, in the Manual of the Geology of India (Vol. I, pp. 368-370), 
of the facts known about the low-level laterito. 
