218 F. Kingdon Wurd—The Land of Deep Corrosions. - 
annual rings of summer and winter wood in a tree trunk, and may be 
put to the same use, namely, to determine how many years it has 
required to build a certain thickness. Summer layers would be 
characterized by greater thickness, coarser material, and plant debris, 
winter layers by sand and mud (glacier mud) without plant remains. 
In the case of a very big river flowing to the sea through a country 
the climate of which was not uniform, these results would be more 
or less vitiated owing to other causes, namely, (1) the creation of 
a reservoir of material at the mouth of the river, and (2) the effect 
of tides in sorting and delaying the deposition of material; moreover, 
the lower course of such a river is invariably sluggish and incapable 
of moving more than the finer materials of denudation. ‘Thus, even 
if the sediment was deposited as quickly as it arrived, no reserve 
accumulating, the uniformity of the material in suspension and the 
selective influence of the tides would effectually mask any classi- 
fication into summer and winter strata based on the appearances of the 
river in its upper course. Thus no such sequence would be detected 
in the case of such rivers as the Yangtze and Mekong, in spite of 
arguments founded on their appearance in the region of the parallel 
rivers, for these rivers are always muddy at their mouths, where 
there are’great reservoirs of silt. But in the case of a river, glacier- 
fed or otherwise, pouring into a big lake in the monsoon region, if 
the river is not too long, and especially if it derives much water from 
melting snow in the spring, seasonal deposits might be conspicuous, 
and it is to such seasonal deposits that I ascribe the interstratified 
sands, gravels, and leaf beds of the Hkamti basin. To continue the 
enumeration of strata passed between Hkamti-Loong and Myitkyna, 
we have, after the sands and gravels: (2) silver-grey (due to the 
presence of white mica flakes), buff, and reddish sands with rounded 
quartz pebbles; friable earths; argillaceous sandstones; blue clays, 
and grey claystones, with leaf beds and nodules of iron pyrites. The 
materials are coarser in the north, gravels, conglomerates, and sands, 
finer in the south, claystones and friable earths, showing that the 
rivers flowed into the lake from the north. The numerous native 
iron-mines in this region probably owe their origin to the accumula- 
tions of vegetable remains. South of the Hkamti plain these soft 
rocks have been thrown up into a series of ridges running parallel to 
the river and to one another, from 3,000 to 5,000 feet above sea-level, 
cut across by rivers flowing from the main divide (the Irrawaddy-— 
Brahmapootra divide, or further south, the Irrawaddy—Chinwind 
divide) in the west. 
8. Crumpled mica-schists, produced from sandstones and giving 
rise to the same friable red earth (or clay) as is derived from the 
sandstones further north—in the bright sunlight this red earth is 
a burnt-ochre colour, and a beautiful feature of the scenery, where 
the dense jungle allows of its becoming visible; and bluish slates. 
The direction of dip varies between south and east, being generally 
about 8.E. or E.S.E., at angles varying from 30° to néarly 90°. 
4. In the bed of the ’Mali-hka just above the confluence, dark 
grey slates with quartz veins, dipping east at nearly 90°. These 
slates probably underlie the lake series, and seem to be identical 
