Page images
PDF

(a).—This bed which we may fairly suppose to have been once co-extensive with the rest of the group is now greatly diminished in area by denudation, which its mineral character even more perhaps than its position at the top of the same has tended to encourage, so that even within the area where it is at present best preserved it by no means constitutes the entire surface, being everywhere deeply scored through to the underlying beds below. The surface is everywhere protected by a gravelly layer composed of small quartz pebbles and ferruginous concretions derived from pebbly strings and irregular courses of conglomerate dispersed through the sand, which readily washing away leaves the residual layer in question at top; to the protection afforded by which against further waste, the existence of what still remains of this incoherent bed is largely due. This surface layer is of Tillable thickness, its development being, to some extent, a measure of the denudation this group has undergone. Ou the surface and impacted in it at different depths where it is very thick lie logs of silicified wood of all sizes from a foot or so to trunks of 40 and 30 feet, not entire, but jointed up into pieces of various lengths through spontaneous fracture, probably brought about by their own weight, and irregular subsidence during the removal of the friable matrix wherein they were originally encased. Though, as a rule, these large logs occur as described in a gravelly debris, they sometimes occur relatively to the incoherent sand so as to leave no doubt of its being the bed wherein they were originally deposited, and on which they may be sometimes seen apparently in situ, as between Thanat-ua and Kiungee, and not only in this bed but in the beds beneath it, the same fossil-wood occurs, though in smaller pieces, and much less abundantly. The larger logs are quite unrolled, but the smaller pieces are often rounded by transport, though never to the extent seen in the pieces of fossil-wood contained in the recent gravels. When this sand rises into hills, the sides are invariably steep, and not unfrcquently scarped, exposing a clean vertical section of sand with its crust of gravel at top. This sand weathers into curious pinnacles wherever an isolated stone, shell, stick, leaf, or other foreign body has afforded shelter from the direct impact of rain, and the incoherent rock all round washing away eventually leaves the protecting substance perched on a slender pinnacle of sand, which recalls the similar phenomenon of the "earth-pillars of Botten" figured by Sir C. Lyell in the 10th Edition of his " Principles."

In color this sand is greyish, very fine and uniform, and with only a certain admixture of impalpable argillaceous matter forming, where exposed to traffic, a fine dust, or, in the beds of streams where the argillaceous portion has been removed by water, a clean silver sand very fatiguing to travel over. Though the sand I am describing unquestionably contains silicified wood, yet it seems probable from the great abundance of large trees strewed over the surface, that they existed more plentifully in that topmost portion which has almost disappeared through denudation leaving only these bulky memorials Dehind it, than elsewhere. The structure of the wood has been to a considerable extent obliterated bj decay before its mineralization was effected, and all that can be definitely said of it is that the wood is exogenous and not a conifer. I have remarked but one species in Prome, though the Burmese, from trivial distinctions in color and weathering, affect to recognise the modern Enjin (Hopea suavaj and the Thiya (Shorea oblusaj, an identification of course quite illusory. This wood nowhere exhibits any traces of marine action as might have been anticipated had it floated about till water-logged in a brackish or purely salt estuary, and hence it may be inferred with considerable probability that it floated about in a freshwater Bea, or chain of lakes fed by a sluggish stream, till it sank where it became ultimately silicified. It must at the same time bo remembered that the wood found in beds containing marine fossils is also free from perforations, but these are small pieces, much rolled prior to their entombment and probably under conditions on some sub-marine bank unfavorable to the presence of either Photos or Teredo. In some pieces of fossil wood I have noticed minute tubular cavities (perforations ?) about '02 or less in diameter, which might have been produced by some insect whilst the trunk was still standing, but such •sses are rare. Associated with this sand, and forming sometimes irregular beds in it, or more frequently lenticular courses, now thickening, now thinning out, occur some hard sandstones, sometimes very fine grained, at others a pebbly grit, or even coarso conglomerate. No regular position in the sand can be assigned to these subordinate layers, but the fine hard sandstone often occupies a high position in the deposit, whilst a coarse conglomerate is not unfrequently ■uet with towards its base. Both sandstone and conglomerate are usually richly charged with shark's teeth of small size (Lamna). the conglomerate being usually ossiferous as well, thnngh throughout the deposit the occurrence of bones is irregular, capricious, and local.

A good section displaying the relation of these grit-courses to the less coherent reck around them, is seen in the hills about three miles east of Shuebandor, or about fifteen miles east of Alan-mio. The hills are here steeply cut in the bed I am describing, the surface being covered with the usual gravel, with abundance of silicified wood and ferruginous concretions, the former completely blocking many of the deep gullies cut on the hill side. Strewed about here may likewise be seen numerous lustrous fragments of iron slag, from the native furnaces once scattered over these hills. The sand here presents its usual incoherent, typical character, but a compact sandstone, passing into a coarse grit in patches, is somewhat freely developed in irregular lenticular courses in it. On the surface of the incoherent sand at this spot, and evidently weathered out of it, I picked up a fragment of the lower jaw of a deer, and from the immediate vicinity I collected mammalian bones, mostly ill preserved and fragmentary, shark vertebra) and teeth, and chelonian plates (Colotsocktks and two species of EmysJ. In the great slabs of grit lying about amidst the debris of the wasting sand which enveloped them shark's teeth were plentiful, accompanying mammalian bones and fragments of wood, many of which had been perfectly rounded by attrition before they were embedded. These pieces of wood are, however, not common. Another locality where bones are still more abundant is one-half mile north-east of Talok, or fourteen miles north-east of Thaiet-mio on the east bank of a stream not marked on the map. Bones are here far from scarce, but friable and ill preserved. They occur both in the incoherent sand and also in the coarse grit and conglomerate associated with it, together with shark's teeth and small pieces of wood. At this spot there is a good deal of coarse conglomerate, and in accordance with the indications afforded by these coarser beds we find the bones of a larger size, and many of these much rolled and abraded before they were finally embedded. Here I got a fragment of the lower iaw of an elephant, together with fragmentary portions of the limb bones of that animal, all imperfect either from original violence or subsequent decay, the former cause certainly operating in some instances.

I may here remark that the bones found in this group (within the area I am now concerned with) are not all in the same mineral condition. The majority are somewhat imperfectly mineralized and consequently decay very readily when bared to the atmosphere by the wasting of the surrounding rock, and this I am convinced is the reason of so few bones being found on the surface, even in spots where the rock is seen to contain them somewhat plentifully. A few fragments may here and there remain, but most of the bones noticed by me were so tender, that it was clear that a short exposure to atmospheric action would reduce them to crumbling masses, which would break up and leave scarcely a trace behind them. A bone is, however, here and there found in the water courses well mineralized and calculated to defy atmospheric action, but the scarcity of these fragments attests that such is not the usual condition of bones in these beds. That these well mineralized bones are derived from the same beds as the more friable ones is undeniable. The best mineralized bone perhaps met with was the part of a deer's jaw above mentioned, and this most certainly was derived from the soft incoherent sand whereon I picked it up. The astragalus of a ruminant (Cervine!) found also by me during a former season, was in like manner an isolated example of well preserved bone, though being found in a small stream its parent bed was not demonstrable. In Upper Burmah well mineralized bones are probably more common to judge by those which have been at various times collected there, and the difference is merely the result of different conditions at the time of their deposition, such as we might expect to prevail, and depending probably on the irregular access or supply of silica in solution. That the supply of this silica must have been at some period abundant is testified by the enormous amount of silicified trunks everywhere met with, but the horizon of these is certainly higher than that at which the bones in question occur, and although small pieces of silicified wood occur commingled with the bones, it does not therefore follow that the same abundant effusion of silica took

Elace at the time of their deposition as subsequently occurred when whole forests were steed, and this I should be inclined to regard as the true explanation of this condition of most of the bones in this sand, viz., an insufficient supply of silica in solution.

As a rule, it is not, however, in the sand but in the coarser and more conglomeratic beds that the bones seem mostly to occur, of which a good instance is seen midway between Omouk and Lema, some 19 miles east-south-east from Thaiet-mio. Here a great bed of

[ocr errors]

conglomerate is seen dipping 30° south-east in which I noticed the tusk of a small elephant, but too friable to be extracted from its hard matrix, together with other bones, all in a poor state, and more or less injured by rolling about on a coarse shingle before their final consolidation.

Next to the presence of silicified wood, a remarkable development of concretionary peroxide of iron seems to characterise the sand I am describing. The ore occurs occasionally is a thin hand, up to perhaps a thickness of three inches, breaking up or jointing into rhomboidal concretionary masses of different sizes and shapes. More usually the ore occurs in the form of variously shaped concretions from one to four inches in length, though occasionally even larger. These concretions are found in both the sand and conglomerate, to which last when numerously developed they impart a peculiar varnished look, which might sometimes be almost styled (but for the technicality of the term) viscous or slaggy. The more usual shape of these concretions is flattish oval or amygdaloidal, but they occur spherical, cuboidal, cylindrical, with both flat and hemispherical ends, discoidal and any intermediate form, but always symmetrically proportioned, and the result of a segregative action or process in the clayey and ferruginous components of the bed when in a plastic condition. Of whatever shape however, their structure is extremely uniform, consisting of an external crust of concentric layers of brown haematite surrounding a kernel of pure white or yellowish clay, lying loose and shrunken in the interior.

Externally these nodular concretions are roughened from the adhesion of the sand enveloping them, but this rough crust scales off readily, leaving their surface perfectly smooth. Internally they often present a blistered appearance from the mammillary crystallization of Limonite which lines them, becoming on exposure to the atmosphere and rain lustrous and varnished. Where the bed has been of too harsh a character to permit the regular segregation of the ore, it is found lining sinuous cavities in the coarse matrix, leaving flat, approximating walls, evidently produced by shrinkage, which gives such portions a very peculiar aspect and one which simulates a viscous condition. In some places even a botryoidal structure is induced where the rock is less coarse.*

The thickness of this upper sand cannot be closely estimated, but 40 feet is probably more than the average thickness of what now remains of it.

(bj.—Below the last described sand occurs a deposit of very uniform character composed of pale silty clay which passes upwards into the overlying sand. This silty clay is very fine, thin bedded and homogeneous, with merely a few strings of sand here and there, and an occasional small pebble in the sand. It is everywhere seen at the base of the last bed into which it seems to pass, though their respective characters constitute a good means of demarcation between them. It is entirely devoid, as far as observation goes, of organic remains. A good section of this silty clay is seen south of Thanat-ua, between Alan-mio and Kiungald, but the bed presents no special point of interest.

It is also largely exposed in section 1} miles east of Talok on ascending out of the stream (previously noticed as unmarked in the map), but it merely presents the same uniform character and absence of fossils, which distinguish it elsewhere. Where the upper sands have been completely denuded so as to leave exposed a large area of this bed, an undulating country is the result, possessing a marked character. The surface of the country does not there greatly differ in appearance from that seen within the area of the alluvium, and it would not

* Under the Burmese rule this ore was extensively smelted, but no furnaces are now anywhere at work in the district. Uemsins of furnaces which were merely rectangular kilns, cut in the firm alluvial clay of some steep bank, which gave easy access at top for replenishing ore and fuel, and below for withdrawing the products, are numerous about Shuebandor, kiungale, and Yebor, together with slag-heaps, sometimes of no inconsiderable dimensions. Throughout the area of these upper sands, however, slag may be found here and there scattered about, as the iron-workers shifted their scene of operations from spot to spot, wherever charcoal and ore was for the time siott plentiful. The works must have in many cases been conducted in the dry season only, as the hearths of some furnaces still standing open into the beds of streams which during rain would certainly have found an entrance to them. The blowing apparatus was probably the effective vertical cylinder bellows formed of large bamboos still in use in the district by blacksmiths, but the oldest inhabitant could give me no particulars of the manufacture, as none of the class of iron-smelters now remain in the district. The introduction of English iron and steel hag doubtless been the main cause of the abolition of this branch of industry, aided by the harsh and injurious system of the Burmese officials during the early struggles with the British, but in some places it was alleged that the ironworkers had fled the country to avoid being forcibly transported to Calcutta to make iron for the terrible foreigners. This mav seem very absurd, but those who know the ingrained credulity and ignorance of Asiatics will be inclined to give some weight to the reason stated, though it is probable that this lear, strongly as it may once have operated, is no longer felt, though the stale of the market and the price of iron now ruling in Pegu prevents the resuscitation of the trade.

be easy in a limited space to discriminate the clay in question from the ordinary alhvial clay of the valley. Where, however, freely exposed, it presents much the appearance of > 'regur,' save in color, which is a pale yellowish-gray, quite devoid of any tinge of red which the alluvial clay generally possesses, and equally so of the dusky carbonaceous hue of > regur. From some peculiarity in its composition or hygrometric qualities it in dry weather opens out in great cracks, and is always covered with a sparse crop of stunted grass in separate tufts, and a tree jungle of a peculiar aspect from the dwarfed character of the trees composing it, present among which are the Toukkian (Terminalia macrocarpa), Te, (Diospyros. sp.), and the " Shabiu" of the Burmese (Phyllanlhus emblica).* The country aroundLaidi comprising the doab between the Pade and Myo-h la streams is composed of this clay with sparing remnants here and there of the upper sands. It is largely exposed, too, in the broad valley about Lepalah (Let-pan-hla) and between that village andChouk-soung ("stone fang"). Towards the mouth of the Myo-hla stream near Toukkian-daing, (Htouk-kyun-deing,) this clay forms the open country and is dug for making potter)-. It might here be readily mistaken for the alluvial clay of the valley, but for the occurrence here and there strewed over it of small pieces of silicified wood derived from the denuded sands which once covered it. The thickness of this bed I cannot estimate, but I should not place it under 40 feet; how much more cannot be determined.

(c).—Below the last described clay, a group of beds occurs of rather varied character, resembling, to some extent, the beds both above and below it. It contains, though sparingly, the same description of fossil wood as the sands at the top of the group, and some of its beds present characters very similar to portions of those beds; whilst towards its base, it appears to pass insensibly into the lower group characterised by marine fossils. It is, however, generally very devoid of organic remains, though, as a convenient lower horizon to it, I have taken a sandstono which is generally recognisable where the j unction is clear, by a few organic remains not very well preserved, among which a coral (Cladocora) is most characteristic, which we may regard as the highest member of the lower group.

A section of these beds is seen in the Kini-choung (Kyeeneech;) above Mogoung, which may be taken as illustrating their general character, and some portions so resemble the

ossiferous sands and gravels of the upper beds that I searched confidently, though in vain, among them for like fossils.

(Descending).

Pebbly sandstone ... ... ... ... seen, about ... 60 0

Pale a'ilty shale ... ... ... ... ... ... ... 3 6

Very false-bedded pebbly sandstone ... ... ... ... ... 16 0

Harsh sandstone, rather irregular ... ... ... ... ... 0 1

Compact yellowish silt with a central band of kidney-shaped nodules 1 to 2 feet

in diameter ... ... ... ... ... ... ... 2 0

Gravelly sand ... ... ... ... ... ... 0 2

Yellow pebbly sandstone ... ... ... ... ... .„ 3 0

Pebbly conglomerate, loose and gravelly... ... ... ... ... (a few feet),

74 9

This section, though not a thick one, will illustrate the general character of the upper portion of this division CcJ. The silty shale much resembles the shale in division b, whilst the sands equally recall the uppermost sands, (a.) Close on the horizon of the above section

* The clay above described and the sandy beds of the same group, respectively, offer good instances of the connection of particular soils with particular kinds of vegetation. So generally does this hold good in Peiru thatia some instances it affords a good empirical criterion of the geological formation beneath. In the area of the fwailwood sands, the most prominent tree is the Eng (Dipterocarjnu grand\flora), and this tree so commonly affect* a sandy soil that the Burmese call such soils, whether within the limits of the fossil-wood sand proper or the rone or detrital accumulations skirting the hills, " Engdaing," or the tract of the Eng tree, and though, of course, Ear tw^ are found on other descriptions of soil, yet it is on this sandy belt that the Eng flourishes most vigorously from probably being there less competed with by other trees, well fitted as it for a sandy soil. The "Thiya" (Shorty Mnm, Wall.) the "Kanyin" (Dipterocarput alata. Wall.) ami the "Engyin" (Sopea tuava. Wall,) equally affect tb? sandy "Engdaing," though not in sufficient numbers to characterize the forest. On the other hand, these tree* abhor the clay described above and are most miserably dwarfed on it. The Toukkian (Terminalia wacroMrpy, though dwarfed, seems to answer best on this clay, but from some cause or other it does not seem favorable to vegetation. I think this must bo due rather to its hygrometric properties, than to any injurious ingredient in it, and that if artificially irrigated, it would give better promise to the cultivator than the densely wooded sands to which it offen so unpleasant a contrast.

Bamboos are not usually much developed on the Engdaing, and a striking demarcation is not unfreqnenllj seen where the Engdaing meets the boundary of the older beds on which bamboos flourish with great luiurumce. The Burmese are fully alive to this fact, and if an enqniry is made regarding a village, say, if It stand within ttw Engdaing, will answer it negatively, "it is among the bamboos," an expression quite equivalent in their minus to saying it is not on the Engdaing where bamboos are rare and never are the characteristic vegetation.

must probably be placed the ossiferous beds, at the top of the river reach above Talohmhor (Keng-yna in map), yellowish sands pebbly at top and passing up into rather soft conglomeratic sandstone containing bones, both mammalian and chelonian, shark's teeth and vertebra, fossil-wood and rolled fragments of oysters and other shells.

A small but instructive section is also seen of these beds in the Myouk Naweng, a little below Thambyagon (Tham-bya-ga-gon), where pale silty shales are seen supporting a great thickness of rusty incoherent sand traversed by tiiin layers of shale and a coarse quartzose conglomerate with clay galls and cavernous hollows incrusted with a layer of the brown hamatite, as seen in some sandy beds of the upper division (a). In this conglomerate I found mammalian bones, shark's teeth, and a small log of fossil-wood about two feet long of very similar character, though less completely mineralized than that found so abundantly in bed a. No other fossils were discernible here, nor, as a rule, throughout this division, though towards its base, sandstones come in containing marine shells and corals, though neither plentifully nor well preserved. These marine beds, however, are naturally more connected with the great group which follows immediately below the present, and which nowhere contains the fossil-wood so characteristic of the present group.

It only remains to add a few words on the very close restriction to the eastward of fossil wood after leaving the area of the fossil-wood group. Nowhere within the area occupied by this group is fossil wood, in pieces of the largest dimensions, more liberally distributed than along the eastern margin of the deposit along which it is everywhere found abundantly, but directly the boundary of the group is passed there is an almost complete absence of fossil wood, even in moderate sized pieces. A very close and careful search in some of the larger nullas may result in finding a piece here and there for some few miles from the boundary, but that is all, and the question at once presents itself,—has this fossil-wood sand extended formerly across the ranges to the eastward and to the Sittang Valley, or was its extension in that direction limited by a boundary somewhat corresponding in its general direction with the present boundary of the group? Without any detailed knowledge of the extent of the group on the eastern side of the Pegu range, we know the single fact that this fossil-wood group occurs in the Sittang Valley, and this and the presumed conformity of it with the lower group which constitutes the bulk of the intervening ranges of hills, would strongly lead us to regard the group as having once stretched uninterruptedly from the valley of the Irawadi across that of the Sittang, or over the entire country bounded to west and east, respectively, by the Arakan and Poung Loung chains. That this must have been the case with the great bulk of miocene rocks so largely developed in this part of the I ra wadi Valley is certain, but one argument, though a negative one, is, I think, sufficient to make us pause before accepting the idea of a continuous extension of the fossil-wood bed over the same area as those of the group below it. This argument is the absence which I have alluded to of fossil wood for a distance not far short of 50 miles, that is, throughout the entire breadth of country occupied by the precipitous hills and tortuous streams of the Pegu range. When we reflect on the large size of some of the silicified trunks which may be said to strew the country along the eastern boundary of this group in Eastern Prome, and the abrupt cessation of any save the veriest traces thereof, and these but for a short distance from the boundary, and consider also the imperishable character of much of this fossil wood as evinced by its abundance in the hard and well worn gravels of the Irawadi Valley, we are irresistibly led to question the former extension of this fossil-wood bed across a belt of country wherein it has left no traces. The evidence is about as forcible as negative evidence can be. Additional weight is also given to it by the fact, that its admission presents no difficulties, hut quite harmonises with the process which the geological history of the district seems to indicate as having occurred. We have only to suppose that the deposition of the vast series of miocene rocks developed in Pegu proceeded uniformly (during, possibly, a synchronous elevation, in a gradual manner, of the ocean bed) till the entire series, save the topmost members, had been deposited. Lacustrine conditions we may now presume to have supervened over portions at least of so large an area, and the elevation of the Pegu range of hills commencing about this time would cause the first land to appear on a low belt of country occupying in its general arrangement the present line of the Pegu range. In other words, the deposition of the uppermost beds of the group and notably of the fossil-wood sands would be arrested along a line of country not greatly differing from the present boundary of the group. The elevation of the Pegu range and its corresponding disturbance of the adjoining strata certainly continued

« PreviousContinue »