PART 4 .] 
Foote: Geology of North Areot Lidnct, 
189 
Alluvial formations. 
the Alikur hills and the N’aikenpalem group. Some of the.se beds are fossil!- 
ferous, and the fossils show them to belong to the upper division of the great 
Gondwana system, which includes all the plant-bearing bed.9 in the peninsular 
area. The fossils agree in many cases, specially with those found in the liajmahal 
beds of Bengal. 
South of the Naikenpalem hills are other outcrops of the “ plant beds ” lying 
between the ISTagari river and the Kortelliar. South of those again and south 
also of the Paliir, the Upper Gondwanas re-appcar in a considerable number of 
small patches dotted over the surface of the eastern part of the gneissic area in 
the Arcot taluq. 
Much of the surface of the “ plant beds ” is masked by lateritic deposits, which 
overlap also in many places on to the gneiss. They do 
Lateritic rocts. cover much ground in North Arcot. One of the upper¬ 
most places in the superposition of the rocks, but the lowest in point of elevation 
over the sea level, is occupied by the alluvial formations, 
which are all fluviatile. Although of very limited extent, 
they yet offer some points of considerable interest. 
The soils are of no special interest, but among the subaerial deposits, the enor¬ 
mous masses of talus which surround the mountains in the north-eastern part of 
the district are remarkable. 
But very little had been written on the geology of North Arcot before it was 
taken up systematically by the officers of the Geological 
Pievious observers. Survey Department. Dr. Buchanan and Dr. Benza had 
given short notes on the geology of the country along the Madras-Bangalore 
road between Arcot and the Mysore frontier, and Lieutenant (afterwards Colonel) 
Baird Smith, of the Engineers, had published a paper “ on the crystalline structure 
of the trap dykes in sienite of Amboor,” entering elaborately into the questions 
connected with the formation of such rocks. 
The geological survey of the district was taken up in 18G3 and continued in 
the years 1864 and 1865, the woi-k being undertaken 
The Geological Smvey. ^ Oldham, hlr. W. King, and the author. 
About two-thirds of the district was surveyed, the greatest part being done by 
Mr. Oldham, who examined the south-eastern and central parts, while Mr. King 
surveyed the north-w'cstern corner. The eastern pai’t north of the Palar, and 
the Vellore and part of the Gudiattam (Goriattirm) taluqs in the south-western 
corner of the district, were surveyed by the author. 
The Chittur, Palamaner, part of the Gudiattam taluqs, and the Punganur 
zemindari, though not surveyed, were traversed in several directions by Mr, 0. AH. 
Oldham and the author, and sufficient is known of them to form an idea of their 
general geological features. 
Of the information gained by the geological survey part only has been 
, hitherto published. So much of the eastern part of the 
Its results how published, within the eastern half of sheet 78 of the 
Indian Atlas has been illustrated in a geologically colored copy of that half .sheet 
printed in 1872. The features of the northernmost part of the district, including 
the Tripatti and Nagari (Naggery) hills, were shown in the small-scale general 
