184 Notes, principally Geological, on Southern India. [Jatt. 



the bifurcation gradually diminishes in ^vidth, till it finnlly disappears 

 in the substance of the rock, after performing an easterly course of more 

 than 200 paces. The second stream is not so wide as the first, and 

 passes through a higher part of the hill. After cutting the summit and 

 giving off one or two minor branches, it separates into a number of 

 ramifications, which spread out, become thinner and shortly disappear. 

 They sometimes cease abruptly, and re-appear at short intervals. Short 

 parallel veins are observed at a litfle distance from, bat having no con- 

 nexion with, the main stream. The>e facts, which I have observed in 

 other parts of India, and the disturbance observable in the rocks in 

 which these dykes intrude, incline me to the belief, that the primitive 

 rocks, in which they are found, must have been in many cases, riven 

 in a nearly solid state by a force from below, the vibrations of which 

 proceede^l nearly at ri!?ht angles with the poles of the earth, and thus 

 formed vents for the liquid basalt, struggling up from beneath. That 

 the imbedding rock is not contemporary, and did not exist in a state of 

 fusion with the basalt, is indicated by the wall -like escarpments, cut 

 shear, as if by the chisel , through the former, into conduits for the escape 

 of the latter. There is here no passage of the one into the other; a decided 

 line of demarcation exists throughout. Yeins of quartz and felspar 

 existing in, and apparently coeval with, the granite itself, are seen 

 divided by the basaltic stream, and solid fragments of the former im- 

 bedded in its course. Others, still larger, are frequently entangled be- 

 tween the ramifications of the basalt ; and, in detached blocks, occasion- 

 ally resemble a vein of granite in the basalt. 



In conclusion of these remarks, I may add that, in dykes of considerable 

 width, both sides of which are bounded by walls of granite, the latter 

 rock becomes altered, as though by igneous agency, whilst the former, 

 on its approximation, becomes compact and comparatively dull, the 

 consequence of sudden refrigeration from coming into contact with the 

 granite. Towards the centre of the dyke the basalt becomes more 

 granular and crystalline, and sometimes porphyritic, imbedding crystals 

 of a greenish felspar : acicular crystals of augite occur in both. The 

 surface has a slightly blistered appearance. Where basalt is found 

 encrusting gnei-s, its edges are found graduating into a thin coat of 

 greenish eurite, the surface of which is frequently vesicular, the cavities 

 containing a yellowish brown powder. This euritic basalt acquires a 

 greyish green hue, imbedding small crystals of epidote and frequently 

 yellow iron pyrites. It also retains a portion of the augite ; exchang' 

 ing the dark crystals of hornblende for the light green epidote. An- 

 gular masses of dislocated granite, with fragments of the basalt adhering 



