1840.] Notes ^ principally Geological^ on Southern India, 137 



coloured felspar, forming an elegant porphyry. Green mossy looking 

 crystals of actynolite may be seen between the porphyry and the em- 

 bedding felspar rock. Veins of a transparent quartz intersect it, and 

 near them occur imbedded cubic iron pyrites ; iron ore in reddish octahe- 

 dral crystals also occurs. Tlie rock imbeds pure actynolite, in long 

 striated diverging crystals, filling up small caviiies, and shooting out on 

 the surface. The rock is remarkably tough, heavy, generally crystalline, 

 but sometimes compact aseurite; translucent slightly at the edges, 

 fracture uneven. The superincumbent soil is red ; beneath it is a de» 

 tritusof ferruginous quartz pebbles, pieces of actynolite slate, felspar, 

 pisiform iron ore, and a few rounded fragments of basaltic greenstone, 

 which exfoliate in concentric layers. In most of the fragments, even in 

 the gneiss itself, I observed a tendency to assume a pentagonal and 

 hexagonal form. I also picked up a crystal of corundum imbedded in 

 a brownish talc. A greyish brown kanker is found on the banks of the 

 nullahs. 



Close to this place, crossing the rocky hills from east to west, 

 I observed a broad dark band descending the hill side, which I 

 took to be a basaltic dyke, since directly west of it we crossed one in 

 the plain, exactly in the line of its direction. This i found to be th(5 

 case on ascending the hill, which was composed of porphyritic granite^ 

 in large unstratified m isses, with crystals of a magnetic iron ore disse- 

 minated, generally grey, but sometimes imbedding shining crystals of 

 red felspar. The summit is crowned by vertical masses of this rock, 

 having a tendency to exfoliate in thick layers. Near the base is a con- 

 vex mammillary mass of the same rock, in which the crystals of felspar 

 and nests of mica had a nearly common direction viz., north and south, 

 following the line of elevation of the hill itself. The dyke of basalt 

 passes completely over it, at right angles with its direction, and is seen 

 Crossing the plain on the other side to the eastward. Its breadth at the 

 base of the hill is about ninety paces, and at the anticlinal line of the ridge 

 about seventy. Over the southern extremity runs another dyke, or a branch 

 of the one just described, of much less width. Both are distinctly 

 visible at a considerable distance passing through the grey cliffs like 

 the dark stream of a muddy cascade. 



From Baugoopilly to the frontier of the Ceded Districts, the for- 

 mation is gneiss, crossed by numerous basaltic dykes, throwing off ra- 

 mifications to the north and south. Flanking the dykes are seen veins 

 of the red felspar and quartz rock, imbedding actynolite slate, and the 

 porphyritic actynolite. The gneiss strata are nearly vertical ; general 

 direction north and south. It is interstraiified with the micaceous horn- 

 blende schist, and intersected by pegmatitic veins of red felspar and 



