Geology and Natural History. 399 
ore pit the limestone on dent oS southward passes beneath 
the slate that makes the wall; toward the bottom its place 
is occupied for a while oe ore ; chen in the same line the lime- 
stone stratum exists again in a short eroded ledg ge, externally 
rusting; and then, again, beyond the ledge, the ore occupies the 
place of the limeston 
.(7) The great spac which is occupied by the ore deposit and 
which is often os eit or more deep, is not commonly a pre- 
viously made cavern; it was made by the dissolving away and 
removal of the limedtene as the oxidation went forward, ere 
the iron derived from the slate or schist no large cavity would be 
b 5S 
schist; and the ore, instead of being pure ore often through 
depths of 40 feet or more, would be mixed with three or fou 
ts weight of ¢ here derived from the aa the fact 
yerno 
ageregation not from the itferencs “i the poe volume of the 
oxide and the iron carbonate, but from the method of its forma- 
remain (clay or sand) to occupy it in prin rt; 
the cavity sometimes becomes hung with atadadeitien Often pro 
there oe per tes crusts made within the limestone. 
(9) The clay of the ore pit is generally in the position of the 
slate or teers from which it was derived, only slipped soniewbiat 
out of place over horse ore in faire cases Diba to the displace- 
e much co 
pressed at the other from the oxidation and decay there in 
te ae and the pressure of overlying materia 
The Pair mkt of the slate has been promoted by the 
eieianis acid set free in great quantities by the oxidation of the 
iron; the cestionatnd week's so made carried away the potash — 
other protoxide bases from the mica and Seton ek and lett 
clay sep eth silicate of alumina) with much undecomposed mica, 
(11 slate or schist of the region contain bat little pyrite 
or me iron-bearing materials to add to the ore of the deposit, 
yet sometimes enough of pyrite to ma rie the miners avoid the 
ore which lies near the schist wall of the ore-pit because of the 
amount of sulphur in it. : 
The ~ conclusions the writer has deduced from his 
observations. The view he is disposed to favor as to the origin 
oa She ella ferriferus areas in the limestone formation is as 
lows: 
The stratigraphical change, in the region, from limestone to 
