84 ON THE WAIANAMATTA SHALES, 
It is to be remarked further that plant impressions of a black 
carbonaceous appearance are found through the sandstone, showing 
an occasional growth of plants on the sandy surface. At any rate, 
in the presence of such plant remains, often with roots, we have 
no other evidence but that of a terrestrial vegetation, and are not 
justified in having recourse to any other hypothesis. The plant 
remains are not aquatic ; and there are strong reasons for supposing 
that Thinnfeldia was a Conifer allied to Phyllocladus (our Celery- 
topped Pine), and not a fern. 
Jornts.—It will be remarked that the shales are conspicuously 
jointed with a uniform direction. Ihave found that the jointing 
YkKES.—All around the Nepean Valley dykes are common. 
It is remarkable that they have disturbed the surface but little, 
and the Hawkesbury sandstone is only tilted a few inches at each 
side, the elevation extending a few yards in a horizontal direction. 
In the immediate vicinity of the dykes the sandstone is metamor- 
phosed into a hard siliceous rock, sometimes not distinguishable 
m the injected material. This is easily understood i 
remember that the sands are felspathic, and probably altered back 
again by heat into the form of the granitoid rock from which they 
were originally derived. The surface portions of both dykes and 
matrix are much altered by water, and these are the only portions 
I have been able to examine. 
Shales on Sydney sandstones.—In a few places around Sydney 
shales are found in somewhat thicker beds than the shales near 
Campbelltown, but they are different in character, and far less 
carbonaceous. They are at least 100 feet lower than any of those 
round the valley of the N epean. 
That they are of the same character as the shales in other 
portions of the formation can be seen from the following section 
obtained in a boring at the Oaks Brickfield, near Neutral Bay :— 
Height above the sea, about 150 feet. 
Sha ae i 16 feet. 
Sandstone... 104 ,, 
Shale ca Hes ied pe as ee 
Sandstone... i ee bce be je BOR 
351 feet. 
The shale here is somewhat of the same composition a8 else- 
where, but less micaceous, and with considerably less carbo: we 
