THE ENTRANCES TO OUR RIVERS. 35 
As to the best system of carrying out such works as are pro- 
posed in this paper, great strides have of late years been m i 
this branch of civil engineering, by the use of Jarge concrete blocks, 
breakwaters having been constructed at a speed altogether 
unknown a few years since. us, 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 avery moderate cost compared with similar work under the 
impossible to carry out except at 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 mattresses made of fascine, which, when sunk in position, 
prevent the sand from being washed out. Layers of stones are 
placed on these mattresses, 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 conclusion, the author’s apology for bringing this subject 
under the notice of the Royal Society of New South Wales is its 
vital importance to the best interests of the coast districts of the 
Colony ; the improvement of the river entrances being the principal 
study of the subject extending over several years, a m 
personal inspection of many important harbours, the author is 
convinced that all that is necessary to ensure success in 
treatment of our different rivers is: “The close observation of 
physical features and effects, and the adoption of means to assist 
e operations of Nature instead of opposing them”—that is (as 
expressed in the charter of the Institution of Civil Engineers), 
“ directing the great sources of power in Nature for the use and 
convenience of man.” : 
. The paper was illustrated by numerous charts and maps, from 
which plates 1, 2, 3, 4, 5, and 6 have been prepared. 
