68 



Azotes, chiefly Geological, of a Journey 



mering (No. 59). Between the seams of the strata, the albite some- 

 times forms a thin stratum of the pure mineral, in needle-shaped crys- 

 tals. Judging by the outline of the hills- six or seven miles west of 

 Poondy, it would seem that they are formed of the same gneiss as that 

 near Carvera, the ravines, down their sides having the same reddish 

 appearance in the places divested of vegetation. 



Leaving this hill, and going north about two miles, in the middle of 

 the road are some enormous masses of porphyry, their surface nearly 

 level with the ground and convex, perfectly similar in composition to 

 the rock of the Garabunda pass, the crystals as large, and as well de- 

 fined. About fifty yards beyond these masses, was a heap of immense 

 blocks of the same rock, many implanted in the soil, while others w T ere 

 placed, tor-like, over the surface of the former. In these rocks the 

 crystals of felspar were better denned and larger than those of Gara- 

 bunda. 



Not more than five yards to the west of these rocks, is a small double 

 eminence, composed of albitic gneiss, similar to that of Carvera, on the 

 little ridge of which were placed many granitic blocks, analogous to 

 those of Guirzinghee. Looking at the direction of the masses of this 

 porphyry, which is precisely the same as that of the pass, it is more 

 than probable that they are the prolongation, under ground, of the 

 same formation. The hillocks and small eminences in other parts of 

 this plain, are either the common gametic gneiss, or that in which the 

 laminar felspar passes into albite ; through which the porphyry at this 

 place seems to have forced its way. 



In conclusion, we may be permitted to make a few general remarks 

 on the phenomena observed during the journey. The first is the sin- 

 gular fact, observed and mentioned by writers on Indian geology, Dr. 

 Heyne among others, of the total absence of organic exuviee in both 

 species ofkankar, which, notwithstanding the different periods of their 

 deposition, are alike deficient in this respect. 



The same remark has been made with regard to the laterite, in which 

 no shells or other fossils have been found, either in the Indian penin- 

 sula, or on the opposite continent and adjoining islands. Such absence 

 is more remarkable, because it is observed of two rocks, the one con- 

 cretionary, the other conglomerate, which appears to indicate an origin 

 not very ancient; and the kankar, in particular, which invests, not 

 only the detritus and small pieces of the unstratified and stratified 

 primitive rocks, such as granite, gneiss, hornblende, chlorite slate, 

 actynolite schist, quartz, &c. ; but also the modern ones, I mean 

 the fossiliferous, such as mountain limestone, sandstone, basalt, &c. 



The lateritic rock at Puddagarum, is the modified heematitic iron ore, 



t 



