ANNIVERSARY ADDRESS. 63 
Triassic, as they are distinctly intrusive into the rocks of the 
Hawkesbury series, it is not quite clear that they are all of the 
same age. It is probable, that in view of the considerable amount 
of denudation to which they have been subjected, they date back 
into some early portion of the Tertiary, or some late portion of 
the Mesozoic era. For example, the basaltic cappings of Mounts 
Wilson, Tomah, King George, and Hay, have probably at one 
time formed part of a more or less continuous sheet ; whereas 
now the Mount Hay outlier is separated from that of Mount King 
George by the valley of the Grose River, considerably over 1,500 
feet deep. No section has as yet been observed shewing any of 
the eruptive rocks in contact with the ancient river gravels such 
as those of Lapstone Hill; but it is probable that the eruptive 
rocks are newer than the gravels. More information on the age 
of the eruptive rocks is much needed. 
©. Folding. No important folds have as yet been observed in 
the Hawkesbury series with the exception of the monocline at 
Lapstone Hill. Foldings however, on a small scale, may be 
observed at many places, as seen in the railway cuttings, in the 
Wianamatta Shales between Lapstone Hill and Sydney. These 
smaller folds are evidently partly the result of superficial expan- 
sion of the shales, due to weathering, as shewn on Plate 2, diag. 3. 
The Lapstone Hill monocline has not yet been systematically 
traced to its north and south limits. Southwards it certainly 
extends for at least three miles, and perhaps continues to beyond 
Picton, a distance of thirty-three miles south. Northwards it 
extends at least as far as the Kurrajong, and may perhaps be 
prolonged so as to join the end of the great anticline south of 
Maitland. Its trend is thus almost meridional. It may be divided 
into three parts, a fold, a septum and a trough; though there is 
of course no hard and fast line between the three. As previously 
stated the sandstone platform has a constant inclination from 
Clarence Siding to Glenbrook of about ninety-five feet per mile. 
At Glenbrook, however, the strata rise to the extent of about fifty- 
three feet eastwards, as shewn on Plate 2, diagram 2, and thus form 
