330 



Granitic Formation of 



[Oct. 



superior elevation to the rising of the granite underneath : another 

 example is the sandstone of the Naggery hills. It has been remarked 

 that while the primitive trap ranges, with the exception of that on the 

 western side (namely, the ghauts), have a tendency N. E. and S. W., 

 inferior ranges supporting secondary strata run more N. and S. — it re- 

 quires observation to prove how far this is the case. 



Where any certain arrangement prevails, it of course affords additional 

 facility in noting down the geological features of any country for refer- 

 ence, and if minor divisions can be effected by septarian lines of a 

 frequently recurring rock, the labour of investigation is divided into 

 parts : the trap ranges being the most regular and constant, would 

 best answer this end. The Tanjore plain, bounded on the north by the 

 Cauvery ranges, and on the west by the Paulghaut hills, forms a very 

 distinct natural division ; while the Mysore region, with the Cauvery 

 ranges on the south, and the Malabar ghauts on the west, is the next 

 succeeding. It is material to observe, that the successive rocks com- 

 posing the area of this compartment, do not terminate in the eastern 

 ghauts at Nakanary, but pass on to the trap chain on the coast. 



Throughout the southern part of the peninsula, igneous rocks great- 

 ly prevail, there being scarcely a trace of aqueous strata ; and among 

 the primitive rocks clay-slate is wanting, r.lthough it is found in abund- 

 ance further north : in certain places clay-slate and limestone tracts, of 

 the transition series, are of vast extent, and, considering the almost 

 invariable presence of valuable metallic ores in such districts, they are 

 not the least interesting in a commercial point of view. 



A careful inspection of the line of western ghauts in different parts, 

 shews that the difference between the two levels has been produced by 

 fracture : a disruptive force having broken the surface of the land into 

 an upper and lower level, as shewn by an abrupt and well defined 

 escarpment. The mountain masses, although in themselves of great 

 size, and originally perhaps of considerable elevation, yet owe the 

 greater part of their height to the same cause ; and it may be mention- 

 ed, that this western fracture appears to have been guided by a previ- 

 ously existing range of primitive trap, from which it does not deviate 

 during its course. We have here the rather unexpected fact, that 

 fractures take place more readily, when the subverted fragments are 

 largest, or where considerable mountain masses existed before : this is 

 not a new observation as applied to direct eruptions, but the same cir- 

 cumstance has not been particularly noticed, as occurring where no vol- 

 canic matter has been immediately erupted. 



The universally vertical stratification of the primitive igneous rock», 

 does not admit of the supposition that they have become concrete in 

 the position they now hold : had such been the case, the stratification 

 would have been horizontal or convex, as seen in the flcetz trap, and in 



