310 BLUE PHOSPHATE OF IRON. 



The production of the blue crystals of phosphate of 

 iron, which are described as so plentiful in this formation 

 in New Jersey, is also an interesting inquiry. They are 

 evidently a secondary product the result of slow double 

 decomposition going on in the soil or in the rock. Iron 

 pyrites abounds in these beds, and sulphate of iron pro 

 duced by the slow oxidation of the pyrites, impregnates 

 the waters that pass through the beds, and renders fer 

 ruginous the springs that issue from them. The contact 

 of these solutions of iron with water containing phos 

 phate of lime, would afford the materials for the produc 

 tion of phosphate of iron, which would be slowly depo 

 sited in insoluble crystals, and of soluble gypsum, which 

 would be carried away in solution by the moving water. 

 This is not an unlikely explanation of the occurrence of 

 the crystallised phosphate of iron. 



But the contact of the same solutions of iron with 

 solid grains of phosphate of lime disseminated through 

 the bed, would produce the same result. This I have 

 proved by experiment. A solution of proto-sulphate of 

 iron poured upon newly precipitated phosphate of lime, 

 washed and dried at 212 Fahr., but not heated to red 

 ness, and left in a closely stoppered bottle for six months, 

 has produced a superficial crust of white gypsum, an 

 apparently unaltered layer of powdery phosphate be 

 neath, and, between those, a beautiful indigo blue solu 

 tion, from which crystals of blue phosphate maybe 

 expected gradually to deposit themselves. 



The presence of crystals of phosphate of iron, there 

 fore, in the green sand of New Jersey, deposited as the 

 result of a decomposition of phosphate of lime, argues 

 the presence of this mineral in the formation, and encou 

 rages the expectation of finding it in quantities which 

 may be economically available. 



Some ten or twelve years ago the Legislature of 

 Pennsylvania resolved, that a geological survey of 



