14 ROYAL SOCIETY OF CANADA 
utilized in this Survey to avoid the multiplication of the principal tidal 
stations. This method is fully explained, with tabulated examples, 
in a Paper on the subject contributed to the Royal Astronomical So- 
ciety of Canada (16). 
Tipe LEVELS AND BENCH MARKS. 
As there is no general system of levels as yet throughout Canada, 
it has usually been necessary to establish a local Bench Mark and to 
originate a datum plane for the tidal observations. Wherever a plane 
of reference had already been established, it was made use of; but it 
is only in two harbours in Eastern Canada that Bench Marks exist 
to which the Admiralty low water datum is referred; namely, Quebec 
and Halifax. At St. John, N.B. all such marks were destroyed in the 
great fire of 1877, and although much trouble was taken to re-establish 
the datum of the harbour chart, the result was only approximate (17). 
At the head of the Bay of Fundy, a good datum was established by 
the engineers. of the Baie Verte canal; and simultaneous observations 
in Northumberland strait connect this with the open sea level. To 
this datum the exceptional tides at the head of the bay are referred. 
An interesting result for mean sea level at the head of the Bay of Fundy 
has been deduced from these observations (18). 
Bench Marks have almost always been established both at the 
principal and secondary stations, even when tidal observations have 
only been continued for a few months. These are valuable at present 
for local reference, and will be more so in future, when they are con- 
nected together by some general system of levels. The Bench Marks 
thus established along the St. Lawrence and throughout the Maritime 
Provinces, are described in a Paper communicated to the Canadian 
Society of Civil Engineers (19). The extreme levels of high and low water 
in the various harbours are there given; as well as the tide levels at 
the head of the Bay of Fundy, which are valuable for the security of 
the extensive hay lands in that region, known as dyked marshes. 
The value of mean sea level at Quebec had long been desired by 
engineers; and accurate local data have now become available there, 
from tidal observations during eight complete years. The relation 
with Atlantic mean sea level at New York was accordingly worked 
out from connections recently made by geodetic surveys and canal 
levels, and from revised determinations made in the United States. The 
result is given in a Note communicated to the Canadian Society of 
Civil Engineers, the data on which the result is based being carefully 
explained (20). 
In British Columbia the levels were in an unsatisfactory condition, 
especially at Victoria. In that harbour it was found that a new datum 
