Page:Madras Journal of Literature and Science, series 1, volume 6 (1837).djvu/381

1837.] generally observable in the fracture, and from one of them I obtained a square prism, which lay at right angles to the walls of the dyke. The texture is compact. The military road running through this valley and down the Bore ghat to Panwell, is frequently crossed by ridges which I presume to be the outcrops of dykes. A dyke is seen on the southern slope of an insulated hill, near the villages of Bosree and Digghee, seven and a half miles north of Poona. It is about four feet thick, has a transverse prismatic fracture, is compact, and runs from the bottom to the top of the hill; but it is not discoverable in the northern slope. It is visible from the cantonments at Poona. A similar dyke occurs in the hill at Ombreh, twenty miles north-north-west of Poona. But the most remarkable dyke runs vertically, from east to west, through the hill fort of Hurreechundurghur. It is first seen, of a thickness of six or seven feet, in the ascent of the mountain on the south-east from Keereshwur, about four-hundred feet below the crest of the scarp. The path of ascent into the fort is intersected by it, and its prismatic fracture, at right angles to its planes, offers a few available steps in the ascent. It is traceable for about three-hundred feet in perpendicular height. On the top of a mountain, within the fort, about a mile to the westward, it is discoverable at intervals, cutting through basaltic and amygdaloidal strata. I could not ascertain whether or not it appears in the western scarp of the mountain, the point to which it directs its course being wholly inaccessible.

The gentlemen whose geological memoirs I have quoted, rarely advert to the subject of trap dykes, and their notices are very brief. Capt. Dangerfield says, "The trap of the southern boundary of Malwa is much intersected by vertical veins of quartz, or narrow seams of a more compact heavy basalt, which appears to radiate from centres." Beyond the continuous trap region of the peninsula, Dr. Toysey notices a basaltic vein in sienite, near the Cavary river at Seringapatam, which must have been propelled upwards, as it broke through an oblique seam of hornblende in the sienite, and carried the pieces up above the level of the hornblende vein. "On the eastern coast," Mr. Calder says, "from Condapilli northward, the granite is often penetrated and apparently heaved up by injected veins or masses of trap, and dykes of greenstone."