CjIAP. I.] riK^■Kl!AL SKETCH Ol'' AREA. 19 



the limits of sheet 79, previously to its being taken up by the Madras 

 party of the Geological Survey of India. 



The earliest writer with whom we are acquainted, who touched 

 upon the metamorphic rocks, was Dr. Benjamin Heyne, of the Indian 

 Medical Service, who in his Tracts on India"^' described the rocks of 

 various places within the area of our report. He frequently fell into 

 the not unnatural error of confounding gneiss with granite and 

 hornblende schist with syenite. He mentions in Tract XXII (Journal 

 of a tour from Bangalore to Trichinopoly in 1802) the spreads of 

 Regur with the underlying Kunkur occurring near Darmahpore in 

 the Baramahal. Referring to the so-called Chalk Hills near Salem, 

 he says, " I have lost the specimen of rock that constituted the 

 forementioned low ridge; in my memorandum I find it was inter- 

 sected by calcareous tuff, and contained in small nests a semi- 

 pellucid greenstone, which, in its decomposed state, in which it prin- 

 cipally occurred, crumbled into a powder which is carbonated mag- 

 nesia. The sound stone is about the hardness of serpentine, and 

 looks not unlike the famous image stone in China. ^^ The soil here- 

 abouts is chiefly a black cotton ground ; foliated hornblende appears 

 often in rocks above it."*^ 



The next author who wrote about the geology of part of the 

 country included in sheet 79 was Dr. P. M. Benza, of the Madras 

 Medical Service, who, in his " Notes on the geology of the country 

 between Madras and Neilgherry hills via Bangalore and via Salem, f 

 touches upon several points in connection with the geology of 

 Salem. He refers to the great number of fragments of quartz scat- 

 tered over the plains near Adamancotta, but failed to notice that they 

 are mainly derived from the degradation of one great granite vein 



* Published in one volume, with maps and plates, London, 1814. 



t Madras Journal of Literature and Science, Vol. IV, page 1 (No. 12, July 183fi). 



(2.11) 



