ifiO 
1 Ik ^\ nni'/rti /I ( i I'ltl nij ixt . 
J). " .'iiiiii'i', iH'.n 
stnilitirapliic niiijie in Hiintiiiirdoii County. Pennsylvania, nrar 
AVani<»r"s .Mark, of at least 1.250 fet't. The whole thickness of 
the Calciferous — Chuzy — Trenton series of liniestones to the i)ot- 
tom of the Hudson Kiver group, there attainino; its niaxiinuni «le- 
velopnient in that State, is estinititeil })y the sanii' authority at 
T.T.")!* fiM'l. A tiiiekness of (i. 011(1 fci't of this series, as esti- 
mateil l»y Trof. A. L. Kwinir. has been reinovetl from the Xit- 
tany A'alley anticlinoi'imn to form that valley, or at least 1,000 
feet in vertical ranee, mainly by chemical ei'osion.''' 
Mcl.'reaths analyses have shown fi'rrons carbonate up to '1\ per 
cent, to bi' widely distributed in Lower Silurian limestones. The 
(piestion arises when this was inti'oduced — whether liefore deposi- 
tion of succeedinjr schists or afterwards? 
That this anhydrous salt was not .directly deposited seems on 
chemical urounds a lmo*it certain. Is it tlicn e\'clusi\-ely a |)roduct 
of replacement of calcic carl)onate throuuh solutions of iron 
salts from extraneous sources, and introduced suljsetpiently to 
en\ clopnient with ferro-siliceous sediments? Or. is it. in part at 
least, the product, practically in lom oriijiiKili. of reactions be- 
tween calcic carbonate in plac;> and vitriolijcinu- parti(des of pyrite. 
oriijinallv reduced from ferroi;s sulpiiate in sea-wat^-r through 
remnants of animal matter in accumulating calcareous sands? 
The researches of Dr. A. .V. Julien into vai'iation of decom- 
position in the iron-[)yrites series, lei him to the conclusion lluit 
till' original condition of iron sulijhi<les along the Appalachian 
helt was that of jiyrrhotite. To whatevi-r degree, in that ease, 
this minei'al may htive sui'vive 1 sul)-a;-rial rock-di'cay. and l)i>en 
uccumulated along with iiower Silurian sediments, would it serve 
as an extremely productive source of iron salts, through decom- 
position 1)\' carltonated waters, inclmling alteration into mai'casiti' 
an<l pyi'itt'. 
Kven this initial traiisfoi'nuition. as indicati'd by Biscliof.t is 
attended liv elimination of 2."). 54 per cent, of iron, and Ijy con- 
traction of volume not less than 152 percent, as estimated from 
relative densities. Hence promotion of permeability in tlu> con- 
tainiu'i rock through d;'\-elopm?nt of cavities. l-'rom sur{)lus 
iron extracted l)y carbonated waters is doubtless developed fer- 
rous carbonate, bv reaction witli calcic carbonate, or else ferric 
*See (ieol. Siirv.. Pa. T... i)p. Alt. -I.U, t.-)4. 
tCavendish K.h. HI, 4.-).->. 
