572 TRANSACTIONS OF SECTION E. 
Further advance in our knowledge of the configuration of our planet can only be 
made by more detailed surveys; and whereas this was formerly impossible, the 
extension of cheap and rapid means of communication into the very heart of the 
explorers’ retreats in all parts of the world renders it now not only feasible, but 
economically desirable. The methods of the past are entirely unsuitable to the 
production of more detailed maps on larger scales; and money must be spent not 
on producing long, narrow, disconnected lines of traverse, but in compact and 
accurate surveys of those areas that most require our study. 
The methods employed will vary in accuracy according to the conditions in 
each particular case; but they will in general be modifications of those in use in 
any organised topographical survey department. At times, even, it may be that 
the methods will be those of the geodesist. As in every other production of 
human effort, increased accuracy means an increasing rate of increase in the cost. 
Before embarking on a survey we must therefore consider well the exact purpose 
for which the resulting map is required. An expert with large practical 
experience and the details both of field and cartographic work at his fingers’ ends 
can ee decide exactly what metheds will economically produce the desired 
result. 
In conclusion, we must not forget that to the explorer, in whatever branch of 
science he may be interested—whether it be geology, botany, or any other of the 
many branches of natural science—accurate maps on topographical scales become 
daily of greater importance; each subject becomes more highly specialised, and 
research is daily made in greater detail than before. 
3. Recession of the Niagara Falls. By Dr. J. W. SpENcER. 
For many years Niagara Falls and the Great Lakes of America have been special 
subjects of the author’sresearches, These have at last been completed under com- 
mission from Dr. Robert Bell, Acting Director of the Geological Survey of Canada, 
and later of A. P. Low, Esq., Director, the results being obtained through precise 
instrumental measurements, borings, and soundings, the last of which had not 
previously been undertaken. The recent survey of the crest-line (1904-5), com- 
pared with that of Professor James Hall (1842), shows the mean rate of recession 
to have been 4:2 feet a year, the average breadth of the gorge produced by the 
Falls being 1,200 feet. But a longer record (agreeing with the more recent) has 
been obtained by Mr. James Wilson and the author in the determination of the 
position of the Falls in 1678, from the crude description and picture made by 
Father Hennepin at that time. Between 1890 and 1905 the rate of recession 
diminished. 
Soundings under the Falls and throughout the gorge were obtained by the use 
of Tanner-Blish self-registering tubes, acted upon by the hydrostatic pressure, as 
the current was too strong for the use of an ordinary line. At the whirlpool, and 
at some other places, it was necessary to work from a cable swung across the 
gorze. Under the Falls themselves the sounding-tubes were inserted in a specially 
designed buoy, which the force of the fall drove down to the rocks that had 
collapsed beneath the Falls themselves. These were reached at 72 feet, while the 
floor of the river beyond varied from 84 to 100 feet below the surface of the 
river. Further down there was a lateral inner gorge, reaching to 192 feet, which 
could not have been produced by the present descent of the Falls. An explanation 
of this, however, was found. 
The river at the whirlpool was measured to a depth of 126 feet; but this was 
not quite in the middle of the current, where the depth is supposed to be 14 feet 
greater. Below the whirlpool the river is shallower. From a short distance 
below the Falls, as far as the whirlpool, the bottom of the channel is at a depth 
of about 90 feet below the level of Lake Ontario. 
At points a short distance within the end of the gorge, and also beyond, a 
narrow, deep, inner channel, reaching to about 180 feet below the level of Lake 
Ontario, was discovered. This established the fact that the aggregate height of 
the different parts of Niagara Falls was more than 500 feet. 
