190 JOURNAL OF SCIENCE, 
and could probably be dealt with by the construction of much less 
stupendous works at a moderate cost. The entrance to the Macleay 
River is one that would require careful study; but as it is well pro- 
tected on the south by Trial Bay, and having a large volume of 
tidal water available for maintaining the entrance, there should 
be no great difficulty in acquiring a satisfactory channel across 
the bar, the entrance to the Hastings River at Port Mac- 
quarie could be much improved, and at the same time a valu- 
able harbour formed, by taking advantage of the sand-bank 
opposite the town, and constructing a breakwater on the north 
in the direction shown on the map. This breakwater would 
protect the entrance from the noith-easterly weather, and at the 
same time steady the tidal current along the south side, thus form- 
ing a deep channel near the town, and by the increasing width of 
the harbour, the force of the waves in the time of easterly gales 
would be broken ; the current at the same time would be focussed 
at the entrance, and be enabled to keep down the bar. With 
skillful handling many of the inlets that are now practically closed 
for navigation might be made available, and those that at present 
can only be frequented by the smallest craft, might be used by a 
much larger class of vessels. But in all cases the first principle to 
be kept in mind is that the battle has to be fought with the waves. 
As to the best system of carrying out such works as are proposed 
in this paper, great strides have of late years been made in this 
branch of civil engineering, by the use of large concrete blocks 
breakwaters have been constructed at aspeed altogether unknown 
afew years since. Thus 710 feet were added to the Manora 
Breakwater, Kurrachee, in less than four months by the use of 
concrete blocks of 27 tons each, placed in position by suitable 
machinery; at the same time this work was carried out at a very 
moderate cost, compared with similar work under the old system. 
Many other instances might be quoted, where, by the use of con- 
crete in its different forms works have been rapidly constructed at 
a moderate cost, that would have been well-nigh impossible to 
carry out, except by an enormous outlay, but for the aid of this 
most valuable material. Another great advance has been made in 
the direction of cheapening such works by the use of large mat- 
tresses made of fascine, which, when sunk in position, prevent the 
sand being washed out. Layers of stones are placed on these mat- 
tresses, which in their turn are covered with other mattresses, the 
work being thus well bound together. This system has been used. 
with great advantage in America, and has recently been adopted 
in Holland, where the extensive works at the mouth of the River 
Maas have been carried out on this system at a very moderate 
cost, and at the same time giving great satisfaction. In conclu- 
sion, the author’s apology for bringing this subject under the 
notice of the Royal Society of New South Wales, is its vital im- 
portance to the best interests of the coast districts of the colony; 
the improvement of the river entrances being the principal work 
necessary to develop the resources of these rich agricultural lands. 
From valuable instruction in the principles that govern the move- 
ments of solid matter held in suspension by tidal and wave-dis- 
turbed water, imparted by Dr. James Thomson during an engineer- 
ing course at the Glasgow University, and trom careful study of 
the subject extending over several years, and from personal in. 
