Chevalier. ] 286 [Jan. 4, 
at most) meters. The rock being thus laid bare throughout a large portion 
of the Channel, it is easy by multiplying the soundings to reach it fre- 
quently with the lead. Then by attaching to the lead a steel tube, sharp- 
ened at its end, we have the means of bringing to light every time the lead 
falls, a small cylinder of the material cut out of it. Success is the more as- 
sured if the bottom from which the cylinder is to be extracted, be of a 
comparatively soft substance, as is in fact the case with the different layers 
of the cretaceous formation. 
This state of things and these circumstances, so favorable to our enter- 
prise, had been already revealed by the experiments of 1875, when, not- 
withstanding the rudely constructed apparatus, and the small and incon- 
venient steamboat, 1528 soundings had been made, 753 of which had 
brought to the surface samples of the material beneath. In 1876, sufficient 
time having elapsed to enable the mode of operation, and the preparations 
incident thereto, to be brought to the greatest possible perfection, and 
when a steamboat was provided, offering all the desirable conveniences, 
6,148 soundings were made, 2,500 of which furnished little cylinders 
cut from the bottom. This makes in all, for the two years, 7,671 soundings, 
and 3,267 samples, of which some however had no scientific value. 
In the same lapse of time the operations were twice as many in 1876 
as in 1875. The little cylinders thus extracted from the bottom of the 
Channel, the character of which was perfectly determined by means of a 
geodesical examination made at the time by Mr. Larousse, were each la- 
beled and enclosed in a vial. They were afterwards examined by the prac- 
tised eye of our geological engineers, Messrs. Potier and DeLapparent, 
who, not content with the mere evidence of the senses, frequently had re- 
course to the precise indications of chemical analysis. They were thus 
enabled in the majority of instances to ascertain to what special layer of 
the cretaceous formation the samples belonged, and in this way the geo- 
logical chart was traced out step by step. 
From the very outset we had felt convinced that the success of a sub- 
marine railway depended absolutely upon the tunnels’ being placed in the 
chalk formation. In this particular we were in full accord with the English 
engineers, who, like ourselves, were occupied with the idea of a junction 
of France and England by means of a submarine railway, and who had 
even preceded us in their explorations, carried on upon the same system as 
ours on both sides of the Channel.’ Outside the cretaceous formation we 
would find a species of rock either very permeable to water, such as the 
green free stone, or of great relative hardness. 
Chalk has the advantage of being easily perforated ; but this cretaceous 
formation is in this respect by no means equally satisfactory throughout. 
There isa marked difference between the upper and lower layers. The 
upper layers, consisting chiefly of a white chalk similar to that worked at 
Meudon, near Paris, contain more or less water. The lower layers present 
qualities much more satisfactory to the engineer, whether he have to cross 
or to remain in them. We have had occasion to note this difference fre- 
