pbnrosb:] PHOSPHATES OF NORTHERN FRANCE. 109 
Greensand, or "Gaize," which is a lenticular deposit lying between the 
Gault beneath and the Sables Glauconieux above. It reaches its max- 
imum thickness of 105 meters near the town of d'Antry. It runs out 
in the north at d'Attigny and in the south near Nettaucourt. It is a 
more or less clayey and siliceous deposit, often containing a large amount 
of silica in a semi-gelatinous form. The phosphate bed lies about 50 
feet from the base of this deposit, and is irregular and undulating. It 
is of variable thickness, ranging from two to twelve inches and averag- 
ing about five inches. 1 The nodules average 55 per cent, phosphate of 
lime and are of the same general character all through the bed. Their 
surface is black or dark green, and is richer in phosphate than the 
interior, which is often simply a mass resembling in every respect the 
Gaize formation surrounding the nodules. In this respect these resem- 
ble some of the English phosphates, which are often found to contain 
50 per cent, of phosphate on the exterior part, while towards the 
interior the quantity of phosphoric acid grows less and less till, in 
the center of the nodule, there is a mass of marly sand or sandy marl. 
The fossils are very numerous and are all much rolled and worn. In 
the Sables Glauconieux, which overlie this bed, there are found very 
similar nodules. They do not, however, occur in a regular stratum, but 
are scattered through the formation. 
The last bed of phosphate, in an ascending series, which is found in 
the Ardennes and Meuse Cretaceous, lies at the base of the Craie 
Blanche (Upper Chalk), and on top of the Marnes Crayeuses (Chalk 
Marl). These nodules differ considerably from the underlying phos- 
phates. They are of a white or gray color, homogeneous in composition, 
and consist almost entirely of carbonate and phosphate of lime. The 
bed is of very little commercial importance, as it is thin, irregular, and 
apt to run out. 
All these French Cretaceous phosphates are very soft and porous, 
and can absorb a large amount of water. They easily disintegrate on 
exposure to air, and are readily ground to an impalpable powder. In 
fact, those of the Marnes Crayeuses are so soft that they go to pieces 
while being washed, and are, therefore, not much used. The French 
differ from the Belgium nodules in having more siliceous matter and less 
carbonate of lime. 2 
The nodules are dug in trenches or in shafts, from which galleries 
thirty to forty feet long are run. They are washed by throwing them on 
a screen over which a stream of water is running, thus reducing the mass 
to from one-half to one-third of its original weight. When water is 
scarce they are allowed to lie exposed to the air until dry, and then 
shaken on a screen. Thus cleaned they retain 10 to 15 per cent, of their 
original matrix. They are then broken and ground. 
1 Nivoit: Assoc, franc, avanc. sci., 1875. 
2 Mr. Nivoit thinks that the nodules were formed by a phosphatic solution coming 
in contact with carbonate of lime either already deposited or being deposited. 
(583) 
