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The term " laterite," as used generally by foresters in Burma, comprises several 

 heterogeneous rocks and soils, all characterized by a more or less ferruginous appearance, 

 but really connected in no other way, than that they are all permeated by hyperoxide of 

 iron : in fact, they derive their origin from two very different sources ; the one being dilu- 

 vial, while the other series is the product of decomposition of underlying rocks. All the 

 laterite along the western base of the Pegu Yomah, and along the Sittang, is decidedly 

 diluvial, but many laterites on the summits and along ridges of the Prome and Marta- 

 ban hills belong to the latter class, which is, especially in Hindustan, largely developed. The 

 influence, however, of all these rocks on vegetation is tlie same, or nearly the same. 



Laterite is a formation of the highest importance in the various floras of India. No 

 other formation except metamorphic and volcanic ones can boast of such a variety of species, 

 in spite of its apparent sterility, as laterite. It is this rock that affects vegetation so 

 much, that the great difference between the floras of Malacca, Borneo, Sumatra, &c., on the 

 one hand, and that of Java on the other side, is produced. It is also this formation which 

 allows so many- Australian genera, like Melaleuca, Bacckea, Tristania, Leucopogon, 8fc., to 

 spread so far to the north-west, some of which, like Tristania, spread as far north as the Ava 

 frontier. If all laterite plants were to be erased from a list of the plants of Pegu proper, the 

 flora would be rendered very uninteresting indeed. 



From about 12 miles S. S. W. from Tounghoo down to Pegu, no true laterite occurs, 

 but a yellowish loam, intermixed with coarse quartz pebbles takes its place. Sometimes the 

 alluvium, here often very light and loose, seems to rest on the sandstone itself. In such 

 localities a strange mixture of evergreens with deciduous forest trees (moist forests) has grown 

 up, changing usually into true tropical forests, where choungs intersect them. The loam 

 soil of yellowish colour, intermixed with small angular pebbles, is especially developed all 

 along the borders of the Pegu and Pazwooiidoung alluvia, stretching down as far as Ran- 

 goon. According to its stitfer or looser constitution, Moist or Low forests prevail on them. 



The gravelly sand soil is predominant in Prome, and not a few peculiar plants occur on it 

 in the Eug forests of that region. The pebbles and sand-granules of that region vary greatly 

 in size in different localities, but all seem to form an impermeable or almost impermeable 

 substratum,* or to rest on such an one. Here boulders and large fragments of fossiliferous 

 calcareous sandstone, of lateritic rocks, and sometimes blocks of fossil wood, are often observed 

 sticking out from the ground or loosely resting on it. 



3. Soft grey sandstone. The next and most important formation, forming nearly one 

 half of the area under consideration, is a soft grey sandstone, composing nearly the whole of 

 the southern range of the Pegu Yomah, from the headwaters of the Hswa choung down to 

 the diluvial formations of the Pegu and Pazwoondoung valleys. Thin layers of older cal- 

 careous sandstone are also found, but only occasionally, as for instance at the obstruction of the 

 Hpyoo choung at Hpyoo-Menglan. But around Kambala toung, the upper part of the 

 Koon and Khayengmathay-choungs, and possibly all around the Prome district, soft and 

 calcareous sandstones are deposited alternately, in thinner or thicker layers. This soft 

 sandstone is everywhere distinctly stratified, the strata, however, are rarely horizontal, 

 but more or less undulating, and more especially so towards the main axis of the Yomah, 

 dipping in the directions of X. E. to E. N. E. and S. W. to W. S. W. at various angles. 



The highest crest of the main range of the Yomah, and all the spurs that compose the 

 Kambala toung, consist of a slightly different coarser pale brownish-grey sandstone, dipping 

 regularly to E. by N. at an angle varying from 25 to 50 degrees. Possibly it is only a de- 

 composed calcareous sandstone, on which at least the Kambala beds seem to rest. 



In.the Yan valley, adjoining Kambala toung on the west, the beds of soft and calcareous 

 sandstones and shales are highly folded, almost contorted and cropping out nearly verti- 

 cally. 



To avoid misunder.standin<, I will remark here, that any hed is to me impermeable, if the constituents of 

 it, whether solid rock, detritus or pebbles, are tliemselves impermeable. Thus a sand-bank, consisting of siliceous 

 pebbles, is in my eyes impermeable, although mechanically quite permeable ; while a similar sand-bauk couaist- 

 inff of pebbles of permeable sandstone, would be doubly permeable, viz., mechanically and physically. 



