BY B. M. JOHNSTON, F.L.S. 77 
portions of the rocky bed which offer any obstruction 
to its downward progress. Geikie happily describes the 
more conspicuous of these rounded polished bosses, exposed 
after the retirement of a glacier, as “ hummocky bosses of 
rock having smooth, undulating forms like dolphins’ backs,” 
and have received the name of roches-moutouneés. One of 
the finest examples of roches-moutonneés in Tasmania 
observed by the writer in the year 1887 exists on the northern 
side of Lake Dixon, in the centre of the narrow valley leading 
down from the ice-scooped lake tarn or basin of Lake Undine, 
lying at the upper end of this elevated valley (2,800 feet 
above sea level). Lake Dixon itself, and several tarns with 
islets near to it, have all the appearance of ice-scooped 
basins. 
4, STRIATED AND PowisHED SipEs oF Precrprtous Rocks 
ALONG THE CouRSE OF A GLACIAL STREAM AND STRIATED 
Buocks AND Stones oF MORAINES. 
The stones carried on the surface of a glacier often fall 
through crevices to its lower surface,or are jammed in 
between the mural edge of the moving ice and the precipitous 
sides of rock along its course, and thus act and are acted 
upon, producing polished, scratched, and grooved surfaces. 
The fixed rock surface markings of striz, lines, and grooves 
record the prevailing direction of the ice stream, while the 
striated boulders and rocks of the moraines afford guidance 
as to the ultimate source from which they have been derived. 
o Hrratics, BouLpERS, AND Forrign Rock Derspris, 
Droprep In Lake on Sea Botroms FRomM FLOATING 
Icz. 
Foreign rocks, both angular and waterworn, may be drifted 
for long distances upon lakes, estuaries, and seas by three 
distinct agencies. 
The roots of fallen trees of great size may be drifted to 
great distances by rivers and estuaries currents, and may 
transport bound up in the ramifying branches of roots large 
quantities of clay and stones, which are eventually dropped 
and scattered as foreign bodies among the ordinary sediments 
and organisms of estuaries or seas. 
The clasping roots of giant forms of kelp and other marine 
Sea-weed may, when storm-tossed, drag and transport for a 
distance the stones upon which they originally grew. These 
Stones are generally polished and waterworn, are of moderate 
size, and show no sign of strie. 
The only known agents, however, which are capable of float- 
ing and transporting to great distances rocks and boulders 
