1836.] 



Southern India, 



333 



understood to have been. The Neelgherries rise from a plain nearly as 

 level as the Carnatic, and their summit bears evident marks of having 

 been once on a level with the Mysore and Coimbatore plains. Like 

 elevated regions in other parts of the world, the Neelgherries shew 

 also traces of a diluvial current ; that is, the gravel and loam are 

 arranged in such a manner as could only take place by deposit from 

 water ; the gravel being lowest in a thin stratum by itself, with the 

 lighter loam covering it, to the thickness of several feet, and without 

 gravel. The carbonaceous black cotton soil occurs here as on the 

 plain, and it is found under the general gravel line as well as above, 

 shewing it to have been lodged among the broken strata, before the 

 passage of the later diluvial current over the surface : the indications 

 are that this current has passed before the hills attained their present 

 elevation, which last seems an event so recent, as to be only anterior to 

 the formation of kankar. As no secondary strata occur near the 

 Neelgherries, none need be expected on their summit; but, onthe eastern 

 ghauts at Naggery, sandstone is found, and serves to point out that the 

 hills there have been elevaled since the sandstone period. It is probable 

 that the other parts of the ghauts have been raised about the same 

 time : every thing tends to show that the elevation of these ranges is a 

 comparatively recent event. 



Taking a general view of the granitic phenomena the following sim- 

 ple geological facts are discernible : that all granite is, on a larger 

 or smaller scale, of a structure distinctly stratified ;* that the structure 

 of granite no where bends from a mountain range under the less solid 

 strata of the plain ; that its position, as ascertained by the direction of 

 its structure, is, like that of the primitive schists, almost invariably ver- 

 tical, and in adjacent fragments ; that the principal mountain masses 

 owe their height to dislocation, and are not original inequalities; that 

 the granite formation, throughout its whole extent, has the appearance 

 of having been perfectly level, anterior to the present dislocations of 

 its crust ; that basaltic dykes penetrating the primitive strata do not 

 expand on the present surface, and, where secondary formations occur, 

 the dyke is not found continued into the overlaying strata — a proof that 

 such dykes existed before the primary strata were broken and sub- 

 verted. 



The structure of the primitive igneous rocks being vertically tabular, 

 extending in right lines quite up to the surface, whether that surface be 

 rugged, smoothly convex, or horizontal, is directly opposed to the 



* It has been maintained that the structure belonging to gneiss and granite ought not 

 to be called stratified, but there is no other term that expresses so well the laminar ar»« 

 pearance of the igneous rocks : schistose will not comprehend the thick bedded varieties, 

 and tabular is more applicable to the mechanical deposits. Mont Blanc is said to be 

 vertically stratified, and its granite contains hornblende. See Bakewell's Geology. 



