152 THE GEOLOGY OF THE LAKE ST. CLAIR DISTRICT. 
which is covered up to the greenstone with a luxuriant 
vegetation of beech (Fagus Cunninghami), sassafras, and 
ferns, etc. The greenstone crest forms a rugged ridge for the 
northern half of the mountain. Running from N.W. to 8.E. 
it terminates abruptly in a mighty columnar wall, and the 
ridge of the mountain is now continued at a much lower level, 
950 or 1,000 feet, above the lake. It slopes down to its 
termination at the Cuvier Valley. This ridge we ascended 
from the lake side, at a distance of about three miles from the 
boat-house on Cynthia Bay. We found it to consist of sand- 
stone from the base to the summit, the beds being almost, if 
not quite, horizontal. The sandstone is of medium texture, 
and rather soft. It forms vertical cliffs along the sides of the 
mountain at various levels, and in many places is weathered 
into caves of limited extent. We were unable to follow this 
ridge to its termination, and so cannot say definitely if the 
sandstone occurs on the summit all the way. It is probable 
that it does, for most of the way at any rate. It appears to 
form the western shore of the lake for its entire distance. So 
much for the eastern aspect of Olympus. 
Passing along Scott’s track up the Vale of Cuvier, we 
crossed over the lower extremity of the Olympus Range. 
Here we noticed masses of sandstone, and quartz-conglom- 
erate mingled with greenstone, but we could not from mere 
inspection decide which was in situ. As the Cuvier Valley is 
followed up, it opens out into button-grass plains of a gently 
undulating and rising character to Lake Petrarch, which, as 
before mentioned, is about 560 feet above St. Clair. Through 
these plains protrude bossy masses of greenstone here and 
there, reminding one of a scene on a Scottish moorland. 
From this side Mount Olympus presents even a grander 
appearance than on the other, and a more comprehensive view 
of the mountain is obtained. The greenstone crest 1s seen 
rising in giant buttresses, and running almost te the N.W. 
extremity of the mountain. During our ascent from this 
side we could not see the character of the underlying rock, 
owing to the dense vegetation and the mass of debris that 
has fallen from the heights above. On our descent, however, 
we encountered at 1,500 feet above St. Clair an outcrop of a 
yellow clayev material, which gave one the impression of a 
sedimentary deposit that had been baked; but we could not 
see its actual relation to the greenstone above. About 200 
feet below this we found several well-marked outcrops of 
sandstone, horizontally bedded, and forming the usual vertical 
cliffs, hollowed out into caves here and there. Springs are 
very numerous along these sandstone cliffs. There seems to 
be no reason to doubt that these sedimentary beds extend 
right along to the N.W. extremity of the mountain, occupy- 
ing the same position relative to the greenstone on this side 
