Tlie Gold-bear'mg Formation of Illinois. — Hershey. 243 
penetrate the same series of strata as at Eleroy, and the basal 
portion of the Utica shales and upper portion of the Everts 
limestone are almost equally as highly mineralized as at the 
other locality. In this case, I could secure no assay cer- 
tificates, but it is a well-known fact that several assayers made 
returns of gold and silver contents of the ores submitted to 
them. 
Between the two "mines" mentioned, the Utica shales, with 
the overlying Hudson River blue clays, etc., underlie an ex- 
tensive tract several miles in average width, part of it forming 
the prominent elevation. "Erin mound." The supposed gold- 
bearing series is exposed in various ravines and gutters along 
the borders of the tract, and is cut through by Yellow creek. 
Everywhere are the peculiar, thin conglomerate layers and the 
high content of iron pyrites. These outcrops will doubtlesslv 
continue to give rise to local gold excitements for many 
years to come ; for I am of the impression that that particular 
portion of the Utica series contains a small amount of gold, 
along with the iron pyrites, throughout the district. 
The facts which I wish to emphasize are that the gold and 
other minerals impregnate one or more strata of a certain 
series, and have no connection with fissure veins, but have 
been deposited in the strata by the simple process of segrega- 
tion under the action of percolating (probably heated) waters. 
The gold must have originally existed, in a finely divided and 
widely disseminated state, in or close to the particular strata 
in which it is now found, and it was afterward concentrated 
and redeposited in the same or a very near portion of the 
strata. There is no reason tO' believe that these mineral so- 
lutions descended through the compact beds of blue Hudson 
River clays above, or came up through the St. Peter sand- 
stone and Galena limestone. On the contrary, we may rather 
suppose that they traversed the strata laterally. de]X)siting 
mainly galenite and blende in the limestone formation because 
lead and zinc minerals were originally disseminated through 
it, and depositing mainly iron pyrites and gold in the basal 
portion of the l^tica formation because these strata had origi- 
nally been sup])lie(l with lliose minerals rather than with lead 
or zinc. 
