19 
absurdly exaggerated, and the disposition of the strata there- 
fore necessarily falsified ; in the other, a true corresponding 
scale for distance and height being adopted, the lay of the beds 
as they actually occur in nature is obtained, and the conclusions 
arrived at are precise and definite. On me devolves the respon- 
sibility of instructing the pupils in the School of Mines in the 
methods by which accurate geological maps and sections are 
constructed ; and it will be my duty to do so, not only in the 
lecture room, but also through the medium of the districts in 
progress on the geological survey, to convey practical instruction 
in field work to those of our mining or engineering students to 
whom such knowledge may be indispensable. 
It would be easy to show many other applications of geology 
to practical purposes, as, for instance, in the construction of 
roads, and the selection of material for macadamising, in the 
engineering of canals by leading them over naturally tenacious 
bottoms and the avoidance of porous formations, in the selection 
of minor deviations of lines of railway with reference to cuttings 
and tunnels, and also in the sinking of shafts. An instructive 
instance connected with shaft sinking came under the notice of 
Mr. Bristow of the geological survey. On the Ridgway tunnel 
a shaft was sunk through 80 feet of sand, which rendered it 
necessary to brick the sides, whereas a few feet further in either 
direction would have carried the shaft safely through the chalk. 
The sinkers had, in fact, chanced to sink in one of those holes 
in the chalk known to geologists by the name of “ pipes.” 
These are always of small diameter, and probably originated 
in the percolation of rain water, the carbonic acid having carried 
off the lime in solution; they afterwards became filled with 
foreign substances, in which, in this instance, they sunk. A know- 
ledge of this simple fact would have prevented the blunder. 
The agricultural applications of geology have been ably 
treated by Mr. Trimmer ; and its bearings on large supplies of 
water to towns are beginning to be universally recognized. The 
country around and beneath London affords a tempting field 
for enlarging on this subject, but at present I shall rather refer 
. to the construction of the artesian well at Grenelle, principally 
because it was undertaken and executed on data and principles 
purely geological. 
5. B 2 
