190 
[voL. xir. 
Beeords of Ihe Geological Survey of India. 
map of tlic region occupied by tlie Kada23a and Karntil rocks, published with ]\Ir. 
King’s memoir on those rocks in 1872,' and the component rocks described in 
that memoir. 
Of the country illustrated in the geological edition of sheet 78 (eastern half), 
only part Inis been described in any of the publications of the Geological Survey 
hitherto issued. 
The part described included the south-eastern half of the Wallajah taluq, 
the eastern part of the Karvet Nagar zemindari, and the south-eastern part of the 
Calask’i zemindari; the description of these was given in a Memoir by the author 
published in 1873.® Brief references tp the three tracts Just named and to the Kagari 
region had been published rather earlier by Mr. King and the author in two 
papers in the Records of the Geological Survey of India, under the respective 
titles, “ On the Kuddapah and KunioolFormations” (1869), and “ Notes on the 
Geology of the neighbourhood of Madras” (1870). Some of the geological features 
of the North Arcot country wore also referred to in a paper “ On the occurrence 
of stone implements in the formations in various joarts of the Madras and North 
Arcot districts,” published in the Madras Journal of Literature and Science for 
1866 by the author, with notes by Mr. King. The same and some other geolo¬ 
gical features of the North Arcot country were touched upon in another paper 
“ On the distribution of stone imj^lements in Southern India,” read by the author 
before the Geological Society of London in 1868 and jraklished in the Society’s 
Journal for the same year. 
The Memoir “ On the Geology of parts of the Madras and North Arcot districts,” 
&c.,® above quoted gave a rather full account of the Upper Gondwana and over- 
lying lateritic rocks in the Arcot district, as also of the alluvial valleys of the 
Nagari and Narnavaram rivers. The information there given will be repeated 
in a somewhat condensed form in these pages, together with a good deal of new 
matter not yet published, owing partly to the non-completion of the survey of the 
district, but mainly to the premature decease of Mr. Charles AH. Oldham. 
The only geological map) on which North Arcot had been represented on an 
intelligible scale prior to the publication of the geological edition of sheet 78 was 
Greenough’s general geological sketch map of India, published in 1854, a laborious 
but in many respects untrustworthy compiilation. The features of the North 
Arcot country are laid down very incorrectly in this map, the data from -which it 
was compiled being utterly insufficient for the purpiose. 
The older rocks of the district being in great measure the source whence the 
materials for the formation of the newer ones were derived, it will be most 
convenient to describe the several groupis recognized in their ascending order of 
sequence. 
* Memoirs Geological Survey of India, Vol. VIII. 
2 Memoirs Geological Survey of India, Vol. X, pt. 1: “ On tLe geology of parts of the Madras 
and North Arcot districts lying north of the Palar river and included in sheet 78 of the Indian 
Atlas.” 
^ Memoirs Geological Survey of India, Vol. X, pt. 1. 
