116 



On the Geological characters, fyc. 



[Julv 



adapted, though it produces a very disfiguring red dust, wher- 

 ever it is employed. This inconvenience might be diminished, I 

 should think, without detriment to the roads, by employing a large 

 proportion of the decaying granitic rock, found in such abundance in 

 the bed of the Adyar river. This rock is binary granite, or pegma- 

 tite, the felspathic component of which is in large proportion, and de- 

 composes into kaolin, or porcelain earth. A large admixture of this 

 with the iron clay, might be an advantageous change from the present 

 system. 



I observe that the active and intelligent Engineer officer, who su- 

 perintends the read department at the Presidency, has made the ex- 

 periment, on a small patch of road, of Mc Adam's system of formation ; 

 and it has succeeded there admirably. The rock he has selected is 

 the pegmatite, in its undecomposed state, and nothing could answer 

 better than it has clone. The spot on which this has been tried is a 

 crowded thorough-fare ; I think it would not answer on the less fre- 

 quented, roads, as the attrition, from the light carriages in use, would 

 not be sufficient to grind down Ihe surface to an even condition. But 

 for bullock bandy roads it would be excellent. 



But, to return to the economical uses of the laterite. As a building 

 material it is not at all in vogue at the present day, though its dura- 

 bility is attested by its present condition in most old buildings about 

 Madras, where it has been extensively employed; as in St. Mary's 

 Church, and some other buildings, in the Fort, and for the piers and 

 coping stones of many of the bridges, over the rivers on Choultry 

 Plain, etc. 



The whole basement of St. Mary's Church is formed of laterite, and 

 the stone has retained the sharpest angle which the chisel gave to it 

 upwards of one hundred and fifty years ago. I think that it would be 

 very judicious, on many occasions, to substitute this iron stone for 

 bricks plastered with perishable chunam, which demands constant 

 renovation, entailing perpetual expense. Twenty slabs, two feet 

 long, one foot broad and six inches thick, may be had in Madras for 

 one pagoda. 



