IN SOUTHERN INDIA, 



305 



published in the Manual, but it appeared in the Becords of 

 the Geological Survey for 1879. 13 



Very interesting geological facts were gathered in the 

 Madras region with reference to the plant-bearing Upper 

 Gondwana beds, the lateritic formations and the alluvial 

 valleys of the Palar and Nagari (Naggery) rivers. Among 

 the older rocks one fact of special interest ought to be men- 

 tioned, namely, that the gneissic rocks are cut up by a 

 marvellous net-work of great trap dykes, chiefly of coarse 

 dioritic trap. These are seen to perfection in the Chittoor 

 country and the south-western part of Cuddapah District, 

 whence they extend up in equal or greater numbers into 

 Bellary District. Such another net- work of trap dykes is not 

 known in India. The size and continuity of these dykes is 

 as remarkable as their ' immense number, and they constitute 

 in many parts a most striking feature in the landscape, 

 forming as they do in many cases the backbones, so to say, of 

 very considerable hills and ridges. 



But very little was known of the plant-bearing beds near 

 Madras when they were first systematically attacked in 1863. 

 They had been visited by Dr. Schlagintweit and Mr. H. F. 

 Blanford, the former of whom discovered remains of a 

 cycadeous plant in the shales near Sripermatur (27 miles 

 south-west of Madras). Beds containing similar cycadeous 

 remains had several years before been discovered underlying 

 the cretaceous rocks in Trichinopoly District, and resting 

 directly on the gneiss. Their distinctness from the overlying 

 cretaceous rocks was only made out after the discovery in them 

 by Mr. 0. 2Ek. Oldham of fronds of Palseozamia (Ptilophyllum) 

 identical with some found in the plant beds in the Rajmahal 

 hills in Bengal which are a group in the Upper Gondwana 

 system. The writer was deputed to examine the representa- 



18 Sketch of the Geology of North Arcot, by R. Bruce Foote, f.q.s.— 

 Records of the Geological Surrey of India, vol. xii, part i, 1879. 



