F. Prime, Jr.—I*monite Deposits of the Great Valley. 439 
the damourite-slate, when, meeting with an impervious bed, it 
could not descend any farther and was then obliged to follow 
the slates. This considerably retarded the rapidity of its flow, 
Deka? the reaction between the limestone (and the carbon- 
ates of lime and magnesia in the damourite-slate) and proto- 
sulphate of iron ws take here more completely. By this means 
carbonate of iron was deposited, being but slightly soluble ; 
while the siphate of ce ayaa formed, being very soluble, 
was carried off in solutio 
No doubt many of the ‘limestone caves—so common in the 
Calciferous limestones—were formed by the gwete. action 
of the water containing protosulphate of iron. The subsequent 
formation of the limonite is easily explained, being pte the 
oxidized and hydrated product of the carbonate of iron. 
n fact, a bed of blue carbonate of iron, identical in appear- 
ance with the ordinary limestone and Friedensville zine- -blende, 
seeks with the brown hematite ores at Balliet’s mine near 
Allentown and at one of the Hellertown mines near Bethlehem. 
t jee: not occur at many of the mines in the Lehigh Valley ; 
those being the only mines where I know of its occurrence. The 
very fact of this occurrence would tend to show that the above- 
mentioned reaction has taken place and was the one by which 
the ore was formed. This reaction would also explain why the 
brown hematites which occur in limestone are almost always . 
free from sulphur, merely containing a trace; and yet almost 
always containing this trace. As a proof of this, I EVs the anal- 
ysis of a brow n hematite fl gird at Katah n Furnace, 
Feng Sonlee Mai The analysis was tek by Pro- 
r'T. M. Drown of pees Collese. It afforded | 
ee H,O and of ae matter SiO, H,S0, P06, 
76°87 19°25 0° 3°10 0°10=100°03 
Professor Drown informs me that the rock underlying the ore 
was siliceous in character, thus giving the sulphuric acid no 
opportunity to combine with lime and be carried away. 
The objection may be raised to this view of the case, that we 
do not anywhere find any deposits of gypsum. It must be borne 
in mind that gypsum is readily soluble, and would be carried 
a i disemne’s in solution before being ae 
I can also point to one very considerable deposit o ator in 
this formation § that of Saltville in Russell County, Virginia. 
It may be urged—and I confess with oo show of reason— 
brown hematite mines at Richmond, Berkshire County, Massa- 
chusetts, there was exposed, about fifteen months ago, a great 
ass of massive carbonate of iron, which was once a part of the 
