RECORDS 
OF THE 
GEOLOGICAL SURVEY OF INDIA. 
Part 4.] 1869. [November. 
On the beds containing Silicified Wood in Eastern Peome, Beitish Burmah, by 
Wm. Theobald, June., Esq., Geological Survey of India. 
No fact relating to the geology of Pegu is better known than the abundance of silicified 
wood occurring in the valley of the Irawadi, but as no detailed account has hitherto been 
published of the beds from which this fossil wood has been derived, it is my intention in the 
present notice to give such a sketch of them as will show their most salient points of interest 
and facilitate the recognition of the group elsewhere, where its occurrence might from its 
mineral character he overlooked and its beds confounded with other and more recent deposits. 
At the same time I shall, as much as possible, restrict myself to the area of Eastern Prome 
and to the fossil-wood group proper, only incidentally alluding to the groat series of beds 
with which it is intimately connected, and on which it rests, as each group has a marked 
facies of its own, is generally, as a rule, easily recognizable and characterised by entirely 
different organic remains, though the balance of evidence as yet tends to prove a passage 
from one to the other and an undisturbed sequence in the beds composing them. The 
fossil-wood group, too, is the smaller and, as regards its organic remains, the simpler of the 
two, and can therefore he treated by itself more conveniently than in connexion with the 
lower, from which the organic remains require much additional study and comparison with 
living species, for which very imperfect facilities at present exist. 
The most familiar form in which fossil-wood occurs in the Irawadi valley is that of well 
rolled and polished pieces of from one to six inches in length, distributed through the coarse 
shingle which underlies the ordinary alluvial clay of the province and is freely exposed in the 
bed of the Irawadi at a variety of places, as, for instance, under the station of Thaiet-mio 
and on the opposite bank under the deserted fort of Miadc. Opposite Prome also a 
great thickness of this gravel, less coarse than at Miade, but equally well supplied with well 
worn and rounded fragments of fossil-wood, occurs, fully SO feet thick, and rising to a height 
of about 60 feet above the present Hood-level of the Irawadi.* 
Besides the ordinarily sized pebbles of fossil-wood, there occur in the gravels towards the 
frontier, as close to Thaiet-mio, for instance, well rounded logs of silicified wood, some two 
or three feet or more in length. These, of course, have never travelled very far from their 
original site, and we accordingly find the parent beds of this quasi-ubiquitous fossil-wood 
in force but a very few miles from the river, whilst irrefragible evidence presents itself of the 
former extension of these beds ovor a much larger area than now occupied by them even as 
far south as Rangoon in the chips of logs of fossil-wood of a size too great for distant 
transport, either resting on some lower member of the group, or encased in more recent 
deposits, the detritus of the beds which originally enveloped them, and with no greater 
change of position than that wrought by the mere action of gravity during the long process 
of denudation going on around them. 
It is not easy very precisely to describe the distribution of this group without reference 
to a map, but in Eastern Prome the area it occupies may he taken at something less than 
* The coarse character of this gravel or shingle, the well rounded and polished condition of its ingredients, 
consisting of the hardest silicious rock, and tiro somewhat mixed size of the pebbles, seem to me greatly iu 
favor of the marine origin of this gravel at a period antecedent to the formation of the present river valley, when 
the sea was wearing away tin siialy rising beds [ am now about to describe, though i cannot so much as guess at 
tlie source of those siiieious rocks of which most of the pebbles consist, so dilfercnt are they from anything now found 
iu the neighbourhood, or I might say province. 
