264 
On Artesian or Overflowing Wells. 
[Sept. 
deposites is principally directed from SE. to NW,, from between Arras and Lille 
to Calais : a little to the south of the last of which, the Cap-blanc-nez consists of 
this limestone. 
By far the greater part of the Artesian wells, which are bored in this district, 
lie to the north of this line, where the newer cover of beds of sand and clay have 
yet attained no great thickness ; and experience teaches us that water is not found 
till the borer reaches as far as the limestone, or has penetrated into it. Few wells 
lie to the south of this line, in the limestone formation itself. But the relations 
of these last are quite the same as tho.se of the others ; they are found, for example, 
in valleys of the formation, the bottoms of which are covered with the same mass- 
es which form the greater plain : we even here do not meet with water till thewater- 
proof stratum of clay, resting on the limestone, has been penetrated. When, 
which is not unfrequently the case, water is met with before this, in the beds of sand 
and loam, its impurity, and the feebleness of its propulsion upwards, shew that it 
is derived from quite another source than the pure water of the Artesian wells. 
From these relations, which are elucidated in Garnier’s work, by the protiles of 
several boring works, it is sufficiently evident that the water, which ascends 
through the shafts, is always derived from the deep-lying points of the limestone 
strata ; from the subterranean slope of the mass of the rock A farther proof of 
the Artesian wells deriving their supplies only from this source, is derived from the 
observations made in several places; as, for example, at Lillers and Betkune; 
that, when one of two adjoining wells, lying in the same line of direction as that of 
the limestone formation, is rendered muddy by the piston of the pump, the water 
of the other is simultaneously milky, from the suspension of minute particles of 
lime. The origin of the Artesian wells can, therefore, hardly be doubted. It is well 
known how numerous and extensive are the fissures, often miles in length, con- 
tained in the limestone of this part of France ; how quickly the rain-water is 
absorbed on the high grounds ; and how abundantly it re-appears, in the form of 
springs, at the foot of these hills 2 . If any proof of this were required from the 
work of Garnier, it only requires to be mentioned that, among the many streams 
of water which issue forth with much violence from the fissures in the limestone 
rock of the steep declivity of Cap-blanc-nez, and which are constantly undermin- 
ing it, s also another proof of the existence of more extensive excavations in this 
district, and which are continually becoming larger, is in the sinking of the ground, 
— for example, in the ajrrondissement of S. Paul, being a not unfrequent occurrence. 
If we now reflect, the iimestone strgta have a position inclined to the horizon, and 
that their outgoing often forms the highest point of the district, there can be 
no doubt that the Artesian wells are only supplied by the atmospheric water, 
2 One of the most instructive instances of the passage pf water through subterranean 
canals in limestone mountains, is certainly, that described by Saussur e (Voyages dans 
les AlpeSj ed, 4. t. i. p. 309), at the Lac de Joux, This little lake in the Jura, 
receives the water of the larger lake of Rouss, and of several rivulets, without its 
haying any other outlet, on account of its bpiqg situate in a valley surrounded hy 
heights, than by the numerous crevices betweeu the nearly vertical strata of limestone. 
On the north-west side, the lake has made for itself a way to them, and has formed a 
deep hollow, by the bottom of which the water is soon absorbed. The inhabitants of 
the valley have also formed similar outlets. As it is very important for them that the 
water maintain a nearly uniform level, they lead the lake, when it overflows, into 
little reservoirs, which tney have dug dowu to the limestone rock, and are eight or ten 
feet hroau, by fifteen to twenty deep, and which they carefully clear from the mud 
which collects in it. One could hardly have believed that these reservoirs, or, as they 
are called there, funnels ( enfonnoirsJ y both natural and artificial, gave rise to the 
springs of Orbe, lying 680 feet lower, and three-fourths of a league from the north end 
ol the lake, if an accidental occurrence, in the year 1776, had not set it beyuud a doubt. 
At that time, the inhabitants, in order to lay dry the little lake, and to clear out its 
outlets hy the en#o7inoz>5, dammed up the lake of Rouss, which empties into it; but 
tnis lake became at onetime so much swollen, that it burst the embankment, and 
rushed downwards with great violence into the lesser one, w hich by that means became 
erv tin *id. I he consequenceof this was, that the usually pure spring of Orbe became 
' ,er an< * ’ m piire. Yet the connexion of the lake of Joux with the springs 
1 se . ems to , a ve been suspected from a very early period, as the stream which 
ni'i f ie two . aes a ^ 0,Fe has also the name of Orbe ; therefore, it has been clearly 
chat i ° ra P ortlou t ^ le fiver which discharges itself into the lake of Neuf- 
ditahtp* in slovenly style in which this paper is done into English, is discre- 
auume to the journal in which it appears.— E d . gl. 
