Fuly 9, 1885] 
to connect the float and the pencil, and this gradually got longer 
by use, and also varied with the weather. Finding it impossible 
to remedy this fault satisfactorily in view of the necessity for 
exact records of the heights of the tides, in 1872 I had a new 
gauze made, which, without losing the accuracy of the time 
record, which the old one possessed, insured the correct 
record of the height of the tides. This instrument is 
figured and described in the ‘ Sydney Meteorological volume 
for 1878,’ and to that work I must refer you for particulars. 
The record by the new gauge was begun on June 27, 1872, 
and at that time the precaution was taken of measuring 
the length of the chain connecting the float and the wheel, 
so that should any change take place its exact amount could 
be ascertained. The wisdom of this has been evident on 
several occasions when the chain was broken by accident, and 
the exact length restored. The well made for the tide gauge is 
in part cut in the solid rock, and from the rock to the surface of 
the ground the sides of the well are built up (round) with solid 
masonry, so that the top ring of the well is practically part of 
the solid rock, and cannot move unless the rock does so. On 
this ring the frame of the tide gauge stands, and the instrument, 
therefore, has a permanent relation to the rock, and there can 
be no change in its parts which might be mistaken for a change 
in sea level. I have been particular in detailing the conditions 
under which the tide measurements have been made, to show 
you that sufficient precautions to ensure accuracy have been 
taken. In each year the mean of all the tides is taken as the 
mean sea level for that year, and when these results for the past 
twelve years are placed side by side, it is at first sight rather 
puzzling, for although the greatest departure from the mean of all 
1s only one inch, yet within this small range the land seems to rise 
and fall in an erratic way. The cause of these variations, how- 
ever, was found in the varying relative positions of sun, moon, and 
earth, and perhaps, to some extent, in the effects of heavy gales. 
Taken as a whole, these results seem to prove conclusively that 
no change whatever has taken place in the relation of land 
and sea during the past twelve years. Of course the question 
is not settled—a slow change that would be visible in centuries 
might be altogether hidden in the results before us; but so far 
as they go these results will be interesting to scientifie men, 
for they are the first that have been taken with such accuracy 
as the investigation demands. Mean Sea Levels: 1873, 2 feet 
5°o inches ; 1874, 2 feet 7 inches; 1875, 2 feet 6°3 inches; 
1876, 2 feet 5°5 inches ; 1877, 2 feet 6°7 inches ; 1878, 2 feet 6 
inches; 1879, 2 feet 5°5 inches; 1880, 2 feet 6°2 inches ; 
1881, 2 feet 5°2 inches; 1882, 2 feet 6°1 inches; 1883, 2 
feet 6°S inches ; 1884, 2 feet 6°95 inches—2 feet 6°11 inches. 
In examining this question I looked for some mark of old 
surveys which might show what the evidence of a Isnger period 
would be, but I have failed to find any mark put in with such 
care as the investigation demands. There is, however, one mark 
on the north-east face of the round tower on Fort Denison which 
was put in by H.M.S. Herald during her survey of Sydney 
harbour. It is cut in the stone three feet above mean sea level, 
and is marked with the broad arrow under it. I have been at 
some trouble to find out on what observations this mark was 
based : but although I have learned that the survey was made in 
1857, and that the Aéral?d was in port from February 26 to 
December 21, 1857, I cannot learn how long the tide observa- 
tions were continued, but I hope still to do so. The time and 
method of taking mean sea level might account for a difference 
from the true mean of four or five inches, as is shown by the 
different monthly means from the recording tide gauge, and until I 
can learn. on what observations the Hera/a’s mark depends, it 
cannot be used as evidence of change of level of the land. I have, 
however, connected it carefully with the zero of the tide gauge, 
and if it exactly represents mean sea leyel in 1857, it proved that 
the land has tisen five inches in twenty-seven years ; but, since 
the tide gauge shows no change whatever during twelve of these 
years, I think the evidence of the mark cannot be taken 
without full particulars of the observations on which it depends. 
In the course of conversation with the late Rev. W. B. 
Clarke on the question of the elevation of the coast, he 
pointed out to me evidence not only of the elevation of this 
Coast, but also of its subsidence, and expressed his convic- 
tion that Port Jackson, Hawkesbury River, and other places 
on the coast had been cut out by the action of fresh water, when 
the coast was much higher than it is at present—in fact, that 
these inlets had been at one time gullies exactly similar in 
characier to those which now exist in the Blue Mountains, and 
NATURE 
235 
which have been so obviously cut out by fresh water. Since 
that time many bridges have been made along the coast, and 
the borings made for foundations for these bridges have 
special significance in connection with Mr. Clarke’s opinion ; 
and by the kindness of the Engineer-in-chief for Railways 
and the Engineer-in-chief for Roads and Bridges I am 
able to quote here some of these measures, which prove con- 
clusively that the sea was at one time much lower than it is at 
present. The soundings taken for the Parramatta Railway 
bridge show 26 feet water, 32 feet mud and silt, 8 feet loose 
sand, 12 feet hard sand, to feet loose sand: total, 88 feet. 
George’s River bridge—8 feet water, 87 feet mud and 
sand, 9 feet black clay, 16 feet sand, 4 feet hard sand: 
total, 121 feet. Hawkesbury River bridge—44 feet water, 
31 feet light mud, 87 feet black mud, 8 feet very hard sand : 
total, 170 feet. In the road-bridge over the Parramatta River— 
41 feet water, 16 feet shells and mud, 15 feet sand, 9 feet blue 
clay, 6 feet clays and shells: total, $7 feet. Ironstone Cove 
road-bridge—26 feet water, 7 feet stiff blue clay, 36 feet very 
stiff blue clay, 15 feet yellow clay, 5 feet stiff black clay, 11 feet 
sand and clay, 2 feet clean sand, 3 feet gravel and wood : total, 
105 feet. Shoalhaven River road-bridge—14 feet water, 103 
feet mud and silt: total, 117 feet. The bottom of the Hawkes- 
bury, therefore, where the railway-bridge is to be, is 170 feet 
below the level of the sea to-day; and when the rocks were 
washed away to form the river-bed to that depth, the sea must have 
been at least 170 feet below its present level, and the bearings 
in Sydney Harbour and George’s River indicate a similar 
fact, if not to the same extent. Without going further into 
this question, which is foreign to my present purpose, I think I 
have said enough to show that the evidence for elevation and 
subsidence of the land are about equal, the question before us 
being, In which direction is the change going on now? Tn esti- 
mating the value of the evidence quoted as to the rate of rise 
in Queensland and South Australia, we must not forget that 
when engineers adopt the usual rule as to mean sea level—that 
is, as to the mean of high and low water at any time of the year— 
they assume that allsuch means are equal or represent a constant 
level, when in point of fact two such determinations of sea level 
may differ by § inches or even more, and in the absence of a 
self-registering tide-gauge, or constant observations extending 
over a year, no levelling referred to the sea in the usual way is 
of any value whatever in such an investigation as that required 
to determine whether the relative level of land and water varies. 
I have already shown that Mr. Ellery thinks there is no evidence 
of present rising in Hobson’s Bay, and the fact that at the time 
the engineering levels referred to were taken in South Australia 
and Queensland there were no self-registering tide-gauges to 
determine accurately mean sea level, is sufficient to warrant us 
in hesitating before we receive the evidence as to the rate of ele- 
vation furnished from these colonies, which I quoted from Mr. 
Clarke’s report. Some few months since it occurred to me that 
it would be desirable to put a self-recording gauge on Lake 
George, with a view of keeping a continuous record of 
evaporation and other changes of level in it; and as soon 
as the instrument could be got ready I put it up on the 
west side of the lake, in front of Douglas House, which 
is about a mile from the present southern end. The work 
of erecting the instrament was completed on the afternoon of 
February 18, and the pencil was put down on the paper 
to begin its curious record at 7 p.m. on that day. At the time 
the lake seemed calm as a millpond, and, looking at its smooth 
surface, no one would have dreamed that such changes were going 
on in it as began to reveal themselves so soon as the pencil 
touched the paper, and in two hours the pencil had recorded a 
rise and fall of about 2 inches. ‘This is not a motion like the 
ordinary wind-made waves, which pass by in two or three seconds, 
but a slow and gradual rise, occupying an hour, and then a cor- 
responding fall in about the same time, to do which a current 
must first have set from north to south for an hour, and then re- 
versed ; and if we consider for a moment the force necessary to 
put a body of water 18 miles long, 5 wide, and 15 or 20 feet deep, 
in such motion, we shall get some idea of the magnitude of the 
forces at work. The record had not been going 24 hours when 
it became obvious that these periodic motions in the level of the 
water had a period of about two hours, and on the afternoon of 
the second day a heavy thunderstorm passed over the south end 
of the lake, and threw a little light on the cause of the pulsations. 
The storm rain was very heavy and much of it must have run into 
the lake, tending to raise the waters there. With the storm there 
