CHAP, x.] CONTINUITY OF THE CHALK. 499 
the sea-bed, was here accompanied by a great abun- 
dance of animal life. | 
I can scarcely regret that the space at my disposal 
will not allow me fo enter at present into the many 
very important bearings of these physical investiga- 
tions, for I am compelled to admit that I do not 
place thorough confidence in our results. The obser- 
vations and analyses were undoubtedly conducted 
with great care and skill, but the difference between 
different samples—in specific gravity, and more espe- 
cially in chemical composition and the relative pro- 
portion of the ingredients—is so very slight, that more 
exact methods than those which have been hitherto 
employed will be required to insure accurate results. 
In such investigations everything depends upon 
the perfection of the means of bringing up water 
from any given depth; and the principle of the 
construction of the water-bottle used in the ‘ Por- 
cupine’ was faulty. It consists of a strong tube of 
brass about two feet in length and two inches in 
internal diameter, containing rather more than a 
litre and a half, and closed at each end by a brass 
disk. In the centre of each of these disks there 
is a round aperture closed by a well-ground conical 
valve, both valves opening upwards when the instru- 
ment is in position for being let down. 
In passing down through the water, a continuous 
current is supposed to raise the valves and run 
through the bottle, thus keeping it constantly filled 
with the water of the layer through which it is 
passing. On reversing the motion in hauling up, 
the valves fall into their places, and the contents 
of the tube at the greatest depth are brought to 
K KZ 
