Page:Notes of a journey across the Isthmus of Krà.pdf/29

 is not absolutely traceable, the close proximity of similar veins is almost certain. In the southern portion of the Tenasserim division, just where in all likelihood the projected canal will be cut, there occurs, he states, a great accumulation of beds of a pseudo-porphyritic rock, resting on the granite and metamorphosed beds. Imbedded crystalline fragments of felspar, which weather out freely or become whitened on exposure, give the aspect of porphyry, from which their name is derived. In their normal character these beds, though highly indurated, are earthy, with the small irregular bits of felspar disseminated in them. They pass, by insensible gradations, on the one hand, into hard, earthy, slaty masses with their disseminated particles; and, on the other, into grits containing many rounded fragments of quartz, quartzite, and these pseudo-porphyritic rocks themselves. The grits often become very coarse and largely conglomeritic ; and the intercalcation and irregular succession of these varied deposits renders the bending of the series traceable. But the rocks have been subjected to very great disturbances, and are found dipping in every direction and at all angles. The higher grounds of the outer ranges in the southern parts of the division, as distinct from the central range of mountains dividing the British territory from Siam, are made up of these rocks, which, however, are feebly represented in the northern portion.

.—These have been pretty fully described already, and a general view of them will be afterwards seen in my letter to Commandant Bellion. The description given by Dr. Oldham tallies exactly with my own. The Eastern boundary, he states, which separates the British territory from the dominions of Siam, is but little known, and is, for the greater portion of its extent, formed by an uninterrupted range of mountains which, in parts, rise to peaks of between 7,000 and 8,000 feet elevation, but the average height of which does not exceed 4,000 to 3,000 feet in the northern parts of the division (Tenasserim), diminishing to 3,000 feet and even less in the more southerly districts. The main direction of the range is north and south, and the direction of the coast line corresponds with this for the upper part of the country, but