390 
GEOLOGY AND GEOGRAPHY 
the intermediate ranges of bills however, over which the route 
to the interior lies, are better known, and specimens obtain¬ 
ed from them shew a highly indurated clay slate as the prin¬ 
cipal form, accompanied by mica slate and other rocks of 
the schistose order. Gneiss is also found in the highest parts 
of the range, and all indicate a close proximity to the granite. 
It is observed that spurs from the main range connect those 
of secondary altitude, which latter have a corresponding par- 
ellelism of direction N. E. and S. W.—the angle of the dip of 
the stratified rocks has not been ascertained, but should sub¬ 
sequent observation shew it to correspond with the same 
formations on the main range, we may from analogous com¬ 
parison be safe in placing granite as the highest rock of that 
mountain system. 
It has been generally assumed, but upon what data I have 
not been able to ascertain, that the range of mountains which 
divides these provinces from Siam, passing on through the 
Malay Peninsula, is a prolongation of one branch of the great 
Himalaya chain. The accuracy of this I am inclined to doubt 
from the observation of the late Dr. Richardson, who stated 
that in passing the border range of hills in latitude 18°, being 
upon one of the highest passes of that range, he observed the 
estimate the whole length of this valley to be 250 miles ; its width, an average 
of 25 to 30. The Thoungyeen, keeping somewhat closer to the Donaw range 
than to the Toungnyo, divides the valley into two long stripcf. The one on 
the left or western bank being held as British, may average about 12 miles in 
width ; the other, or Shan, about 15 or 18. 
“ Both the bounding ranges of Donaw and Toungnyo, together with their 
spurs, consist of mountain limestone, presenting all the grey and grotesque 
appearances and cavernous issues of sudden waters (many at a high tempera¬ 
ture) so characteristic of that rock. Their highest portions again are of 
granite, but of a composition in which the felspar greatly predominates ; the 
quartz and mica being in very subordinate quantities. It is for this reason 
the weathered peakB get very rapidly disintegrated, the felspar rapidly de¬ 
composing into Kaolin clay ; the fracture of such points presents the dead 
even appearance of a clay rock, rather than the sharp and angular edges of 
true granite. 
It is from the disintegrated felspar of these weathered peaks that were 
probably, in a great measure, once supplied the deposits of stiff clay, which 
we find playing so important a part in the economy of the Thoungyeen forests. 
These ranges are also said to be metalliferous. 
The great underlying rock is most probably the mountain limestone, of which 
the Donaw and Toungnyo hills are composed ; but in the valley'itself this no¬ 
where obtrudes itself to view. We find there the lowermost rock to be a compact 
sandBtone, the upper portion consisting of a concrete of small rolled pebbles 
imbedded in a siliceous matrix. On this reposes a deposit of large rolled 
pebbles, the depth of the bed varying from 8 to 14 feet. On this again, and 
of about the same thickness, is a bed of stiff pure clay, supporting a layer of 
“ humus” or soil proper, of from a few inches to a foot in thickness. 
These strata are generally quite horizontal, except in the upper Thoungyeen, 
where the sandstone has a dip of about 35 degtoes.” 
