86 REPORT—1857. 
older of these two groups (the Mergui) we have no data. ‘The aspect of much of the 
rocks is very similar to the trappean ashes and felstones so abundant in the Silurian 
rocks of this country, while others are lithologically like Devonian; but these resem- 
blances are very deceptive. The age of the Moulmein series is, however, tolerably 
defined by its organic contents. ‘These appear to fix the age of the group as distinctly 
carboniferous. ‘The whole of these rocks were, subsequently to their induration and 
disturbance, widely and greatly denuded, and on their upturned edges at intervals is 
found a series of conglomerates and sandstones and imperfectly coherent shales, with 
thick beds of coal, generally of lignitic character. None of the conglomerates are 
coarse; the sandstones are fine, gritty, and pebbly, or clean white quartzose grits ; 
ihe shales thinly laminated; the coal itself thinly disposed in thin flaky lamine, with 
eaithy streakings marking its structure. In addition to the total unconformity of 
these rocks, the imbedded organic remains are quite distinct. They consist of dico- 
tyledonous plants (leaves) belonging to the group of the Iaureacez, and probably to 
the genus Lawrophyllum of Goppert. In the thin papery shales which overlie the coal 
are also remains of fish (scales, &c.) of freshwater character; the whole referring the 
beds to a very recent epoch, probably corresponding in part to the pliocene of Euro- 
pean geologists. It is curious to notice here the absence of any coal in the carboni- 
ferous rocks below, and its abundant presence in those newer beds. ‘The total thick- 
ness of these beds does not exceed 900 to 1000 feet. They are never continuously 
traceable; they occur heaped up against and separated by the projecting ridges of the 
higher grounds, and must have been deposited when the physical conformation of the 
country was very similar to that now existing. They appear to be the result of a 
series of freshwater deposits, formed in small lake-like expansions along the lines of 
the great drainage valleys of the country; and to mark a line of general and greater 
depression between the main ridge of hills dividing Siam from tie British dominions, 
and the outer ridges which occur between this and the sea. The direction of the. 
main drainage of the country is determined, as already remarked, by the direction of 
these ranges, and is discharged into the sea through narrow rocky gorges, which 
have a direction nearly east and west, and which are due to lines of breakage and dis- 
location. To this is due the sudden alteration in the direction of the courses of the 
larger rivers, as may be seen on maps. Rocks similar to those situated in the Tenas- 
serim provinces extend northwards up the course of the Salween River, and into the 
adjoining districts of Burmah, to the north-east of Pegu. And, again, close to the 
capital of Burmah, and stretching nearly north and south, as far as examined, high 
tidges of metamorphic rocks are again met with, consisting of gneiss, micaceous 
schists, and highly crystalline limestones, occasionally of a fine white colour, and 
largely used by the Burmese for sculpture. But the great valley of the Irrawady is, 
throughout a very large extent of its course, bounded on either side by a thick series 
of rocks, chiefly sandstones, but with massive limestones also, which are locally rich 
in fossils, and which, from this evidence, may be clearly referred to the eocene period. 
These stretch on both sides of the river as far north as Pugahu, beyond which the 
higher grounds recede from the river banks; but they are in all probability continued 
thence into Munipoor, and so united with the nummulitic rocks of the Khasi and 
Cachar Hills. These rocks have been considerably disturbed and broken, but have a 
general and prevailing strike nearly north and south, which strike, throughout many 
miles, has determined the general course of the River Irrawady. Their thickness 
is considerable, certainly exceeding 5000 feet. Above these eocene rocks, and rest- 
ing upon them with slight unconformity, is a series of beds of no very great thickness, 
characterized by an abundance of gypsum disseminated in thin layers and veins, and 
in the lower beds of which occur the deposits of clays and of vegetable matter, from 
which are derived the larger supplies of petroleum. ‘These rocks are well seen at 
Senan Kyoung (‘stream of fcetid water”), and are traceable northwards to near 
Amarapura. In the beds which appear to form the uppermost part of this group, but 
which may possibly belong to another and distinct series, are found some of the fossil 
bones of the larger animals which occur abundantly in this district, About forty 
miles north of Amarapura we again meet with sandstones, shales, and coal, resting un- 
conformably on the metamorphic rocks, and characterized by remains of dicotyledo 
nous trees similar to, if not identical with, those found in the coal-yielding group of 
the Tenasserim provinces, and which are therefore referred to the same age (pliocene), 
ee... 
