48 T. W. E. DAVID. 
at this spot, according to the Challenger Reports op. cit., is eighty 
fathoms, which would throw the outcrop a little over two miles 
further eastward, that is to about eighteen miles from the coast, 
if the seam outcropped in the actual floor of the ocean. It is just 
possible that it may do so as “hard ground and shells ”” were 
reported near this spot by the Challenger, and this “hard ground” 
may represent an outcrop of the coal-measures. It is much more 
probable, however, that the outcrop is covered partly by recent, 
and partly by Tertiary, marine deposits. As Mr. OC. S. Wilkinson 
has remarked, (op. cit.) the absence of any marine Tertiary 
deposits along the costal area of New South Wales, is probably 
due to the ocean bed in which they were laid down having par- 
ticipated in the supposed subsidence of the coastal area between 
the Lapstone Hill monocline and the edge of the continental shelf, 
Marine Tertiary deposits, attaining a thickness of upwards of 
five hundred feet, partly of Eocene and partly of Miocene age, 
are developed in Victoria, Southern South Australia, and Tasmania 
and it is almost certain that conditions favourable for the depo- 
sition of similar strata must have obtained in N.S. Wales also 
during the Tertiary era. The absence, therefore of Tertiary strata 
from tle eastern coast of New South Wales is only to be explained 
on the hypothesis that they are now submerged. A thickness of 
perhaps five hundred feet might be assumed for these Tertiary 
strata, and to this might be added a further thickness of perhaps 
one hundred feet for Post-Tertiary deposits. If this theory as to 
the structure of the continental shelf, at the point where the Bulli 
seam outcrops, be correct, it would follow that the concealed out- 
crop would have to be located about five miles nearer Sydney than 
the distance above quoted, that is, it would have to be placed at 
thirteen miles instead of eighteen miles east of the coast. Obviously 
any increase in the angle of dip of the coal-seam between the coast 
and its concealed outcrop would have the effect of bringing the 
_ latter still nearer the shore line. It is improbable, however, that 
the outcrop is nearer than ten miles, or further than fifteen miles 
from the coast. 
