penkose.J PHOSPHORITES OF SOUTHWESTERN FRANCE. 51 
the deposits were formed by a solution of phosphate of lime in carbonic 
acid, running from the surface downward into the fissure. When all 
the fissures were filled the solution often spent its strength in plios- 
phatizing the marl of the neighborhood. Thus at La Mandine Basse 
they find a calcareous marl containing 23 to 30 per cent, phosphate of 
lime. 
Mr. Combes 1 thinks the phosphate bed was formed by phosphatic 
vapors rising up through the Jurassic limestone and phosphatizing it. 
He thinks a similar action is going on at the present time. Mr. Malin- 
owski 2 thinks that the beds are of purely animal origin and that vol- 
canic eruptions of Auvergne killed all the animals of the period and thus 
furnished the phosphate to fill up the fissures. Mr. Delfortrie 3 thinks, 
the deposit is of Quaternary age and derived from altered guano. 
Mr. Peron* has shown that the phosphate deposits only occur where 
the Tertiary deposit now exists or where it has existed in time past. 
Thus on the Jurassic plateau at Bach, Mouillac, and Malperie, the Ter- 
tiary formation which covers it at Lavaurette, Monpalach, and Lasalle, 
in Tarn-etGaronne, has been eroded. Yet both districts are rich in 
phosphate. On the other hand, at Laussiers and Anglars, where he 
supposes the Tertiary has never existed, there is no phosphate. He 
thinks the phosphate deposits are synchronous with the Lower Ter- 
tiary of Aude and Tarn. The waters of the Eocene, he supposes, came 
suddenly over the Jurassic plateau, overwhelming the numerous land 
animals of the region and sweeping the remains of these and masses of 
guano into crevices and cavities, together with quartz pebbles, land and 
fresh- water shells, and other debris. Then the action of time and car- 
bonated waters partially metamorphosed the phosphate and converted 
it into concretions and other forms of phosphorite in the midst of the 
clay and bones. At a later time the ^superficial deposits of bones were 
laid down. 
The strongest arguments of the advocates of the hydrothermic theory 
are the presence in the phosphorite deposits of iodine and manganese, 
and of pisolites of iron, which are generally of hot spring origin. 
Peron thinks these latter were formed during the deposition of the 
Lower Tertiary formation. He also calls attention to the fact that phos- 
phorite has nowhere been found in the southwest of France at a greater 
height above the sea than 320 meters. This he explains by supposing 
that the waters of the early Tertiary did not extend above this height. 
The phosphorites of the southwest of France were discovered in 18G5, 
on the plateau of Quercy, in the department of Lot, by Mr. Andre Pou- 
niarede. Five years later the deposits of Lot-et-Garonne, Tarn-et-Ga- 
ronne, and Aveyron were discovered and worked until the last few years, 
Phosphorites du Quercy, Revue scieutinquo, 1872, No. 12. 
' 2 Traite special des phosphates de chaux natifs, Cahors, 1873. 
3 Les gifcesde chaux phosphate^ dans le depart, du Lot, Bordeaux, 1873. 
4 Bull. Soc. g6ologique France. 2d series, vol. 2, 1874. 
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