GEOLoa y. 5 



leave tlie lulls, spread in sheets over the plains, farming huge inlaiul hikes, so 

 that on the turbid waters of the river rising, they are prevented from sprcadinr>- 

 far from the banks, in spite of the flatness and low nature of the ground, l)y these 

 depressions in the surface of the country being already occupied by water from 

 the hills, which by the end of the rainy season has acquired a clear brownish 

 colour, from decomposed vegetable matter in solution, but which deposits next to 

 nothing on the area covered by it, and from which all intrusion of turbid river- 

 water is efl'ectually barred. 



INTRUSIVE ROCKS. 



Under this head are included all rocks of a plutonic or volcanic character, 

 granite, trap, basalt, lava, serpentine, etc. Some rocks related to this class as 'ash- 

 beds,' though the product of volcanic agency, are spread out contemporaneously 

 with the beds wherein they occur by the action of tlie waters beneath which they 

 were erupted. Beds of this class (ash-beds) are frequently not easy to distinguish 

 from ordinary sediment.ary deposits, and are rare in Burma, but a small patch 

 occurs in Promo district at iMinet-toung or the ' black hill,' so called from the 

 colour of the surface soil, which precisely resembles the reijitr, or black cotton 

 soil of India. Tliere are three spots where this rock occurs; at two 'Minot-toungs ' 

 the ash-bed, a contemporary trap as it is in part, forms the top of the hill ; whereas 

 in the third, the dark line marks the outcrop of the same bed inclined at a 

 considerable angle and clearly intercalated in the Tertiary series. 



Granite. — This rock does not occur west of the Tsittoung, but east of that river it 

 is largely developed, and gives rise to very picturesque scenery. It stretches away 

 north beyond the British boundary up the Salween valley, and down south through 

 the Tenasserim Provinces into Siamese territory. This gre.it belt of granite is 

 remarkal)le as the rock wherein the tin-stone is imbedded, which forms one of the 

 most valuable mineral products of the country. Tbere are no workings of this 

 ore in Blartaban, thougli just across the border it is worked by the Karens, and 

 the metal run into the form of small pigs of about a ' viss ' in weight eacli ; but 

 there seems reason to believe that the ore occurs within the British territor}' also, 

 though in a wild and thinly-inhabited country. The ore is also known in Tenaa- 

 serini on the streams falling into the Ilenzai basin, and will probably one day bo 

 worked with protit when the country becomes moi-e accessible and populous. 



TuAf, Basalt. Greenstone. — These rocks may be said to be unknown west 

 of the Tsittoung, but dykes of them traverse the metamorphic rocks east of that 

 river, and in Tenasserim ; they are not, however, largely developed, and call for 

 no special notice. 



Serpentine. — This rock is met with in Pegu at various spots in the Arakan 

 range, mainly on the east side, that is, within the Trrawaddy valley. These outbursts 

 form three principal groups; the hills cmnposed of this rock being remarkable for 

 their sterile aspect. The most northerly mass constitutes a horse-shoe-shapod in- 

 trusion forming Bidoung hill nearly due west of Thayet-myo. Several masses also 

 occur north-north-west of Prome, one of which forms a long dyke-like mass running 

 for about five miles along the boundary of the Nummulitic and 'J'riassic rocks, 

 with the appearance of altering the latter, but not the firmer, though they are 

 much crushed, indicating therefore that the newer rocks are brought in contact 

 with the serpentine by a fault. Another group of upwards of twenty-one isolated 

 serpentine intrusions occurs west of Henzad.a, scattered over a length of twenty-six 

 miles in a north and south direction. The largest outburst is three miles in 

 length, but the majority are less than a mile in diameter. Associated with the 

 serpentine, and as though the result of its action on the neighbouring rocks, 

 occurs a great deal of the soapstone (kfnhjn) used liy the Burmese for writing. 

 The mineral is identical with that imported from Upper Burma, and occurs in 

 veins associated with fibrous quartz, the two being much interlaced. In some 



