GEOLOGICAL NOTES 
By J. REYNOLDS. 
The Mount Field range, which is almost 
entirely included within the limits of the 
National Park, is composed of a mass 
of igneous rock, of the same origin, iden¬ 
tical in its composition, and contem¬ 
poraneous In its intrusion with the other 
prominent mountain ranges in Central 
and Southern Tasmania. Although inti¬ 
mately related to the neighbouring moun¬ 
tains, it nevertheless apparently stands 
isolated from them, and a:s far as dis¬ 
cernible. it is unconnected in any way 
with the Mount Wellington range. Mount 
Meuller. or the great cordon of peaka 
which flank the Central Plateau. lie 
garding the detail*, of the intrusion of 
this rock mass into the then existing 
sedimentary rocks, little is accurately 
known to-day, but it is certainly a local 
manifestation of the worldwide igneous 
activity late tu the Mesozoic period. 
The sedimentary rocks were lifted bod¬ 
ily to such an elevation where they be¬ 
came exposed to the full severity of the 
climatic conditions. In the great space 
of time which elapsed since their ele¬ 
vation and the beginnings of the Pleis¬ 
tocene ice age great quantities must have 
been removed by the ordinary agencies of 
denudation. Only in the valieys of the 
lower level?, as in the vicinity of Rus¬ 
sell Falls, and the Florentine Valley, on 
the other side of the range, are these 
rockg to be found in any quantity to-any. 
To take a bird’s eye view from Uia 
ridges which are crossed by the Mount 
Field west track, a glacier flowed down, 
tearing out great boulders, and pushing 
before it immense quant it ies of ro *ks 
and gravels. It worked Its way down 
to the edge of the plateau, where before 
descending it wore out the depressions 
which now form the picturesque little 
tarns. The descent to the valley, an 
almost sheer drop of about 1000 feet, 
must have been most rapid, and hero 
by attaining its greatest velocity it 
exerted its greatest erosive power, form¬ 
ing at the head of Lake Seal, a perfect 
example of a glacial cirque. After the 
descent it pushed its way down the valley 
of the Broad River for nearly a mile, 
when it was met by another glacier whi Mi 
had it? origin among the heights of Mount 
Mawson. Where these two glaciers junc¬ 
tion ed. near Lake Webster, there occurs 
a great accumulation of rocks of all sizes. 
Still another glacier flowed down from 
me heights ahove Lake Seal This one 
in its course, like the first mentioned, re¬ 
sulted in the formation of two tarns - 
Lake New degate and Walker’s Tarn. 
Thence in descending it scooped out. a 
U-shaped valley terminating in a cirque 
above Lake Webster, afterwards joining 
the other glaciers in the vat Icy. 
With climatic conditions becoming less 
extreme the ic** melted, and the glacier* 
In receding dropped their immense bur - 
dens.. As the giaclers successively re¬ 
treated back uj> the broad River valley 
they deposited great thicknesses of red¬ 
dish brown clays (boulder clay or till), 
which lies under the surface, whilst above 
can be easily seen the low ridges of 
boulders and rocks and morruiual ma¬ 
terials which bridge the button grass 
slopes of the valley in numerous places. 
Where a glacier deposited a considerable 
quantity of Its burden in such p. manner 
as to dam Up the valley It has itself 
scooped out. A lake was formed, and this 
was the factor which resulted in the 
formation of Lake Seal and Lake Webster 
in this locality and other lakes in the 
adjacent portions of the park. Lake 
Dohson, on the other hand, seems to have 
just been formed by the damming up of 
a small valley, and net deeply gouged out 
as in the case of Lake Seal by a small 
glacier flowing down from Mount Maw¬ 
son. All down the Broad River valley 
ere to he seen great numbers of rocks, 
some of very considerable size, which 
have been broken off the mountain sides 
and transported down, where they have 
been deposited as “erratics. M Some, how¬ 
ever, have only been carried a short dis¬ 
tance on their downward journey, and 
are found to day perched oiten in the 
most precarious conditions high up on 
the mountain sides. 
Whilst the Broad River valley is a 
veritable museum of glacial remains, 
other portions of the park afford strik¬ 
ing examples of glacial action. From tli0 
ire-cap on Mount Field East several 
smaller glaciers flowed down to the low'er 
levels, and have left Interesting evidences 
of their notion. One flowed over Kanga¬ 
roo Moor down the valley between Sen¬ 
der's Lookout and Mount Monash, deep¬ 
ening and carving it into a U shape. A a 
it receded it deposited most of its burden 
18 
