244 '^f''^ American Geologist. October, i899 
In explanation of the large amount of iron pyrites in the 
basal portion of the Utica shales, and its rarity in all the other 
formations of northwestern .Illinois, I have adopted an old 
theory which has often been urged in similar cases. I notice 
that the Utica shales of Stephenson county yield traces of 
sea-weed impressions, and the whole formation appears to be 
largely made up of vegetable debris. Some layers, also, are 
thickly packed with the remains of minute marine animals. 
The Utica formation in the Eleroy-Pearl City district seems tu 
have been deposited in a shallow bay rather than under deep- 
sea conditions. This favored the growth of marine vegeta- 
tion, and also its subsequent decay. Is it not possible, indeed 
more than probable, that the sulphurous gases resulting from 
this decaying vegetation and animal matter, forced and pre- 
cipitated the iron (and possibly the gold) salts contained in 
the sea-water, so that these minerals came to make up an 
important original constituent of the Utica shales of this 
district? 
It has been stated that in the Eleroy "mine" the gold is 
chiefly found in certain limited quartz-filled cavities in one 
particular stratum. Here the limestone has been dissolved 
out in spots and the spaces thus formed, simultaneously filled 
with quartz in which the gold, gathered throughout the 
stratum, was deposited in a concentrated condition. This 
was affected simply by water oozing through the pores of the 
rock, or, in other words, by segregation. 
April 7, iSgQy Freeporty Illinois. 
A DISCUSSION ON THE USE OF THE TERMS 
ROCK-WEATHERING, SERPENTIN IZ ATION, 
AND HYDROMETAMORPHISM.* 
Hy Geohge p. Merrill, 
Head Curator, Dept. of Geology, U. S. National Museum, Washington, D. C. 
In the abstract of a paper by Mr. Thomas H. Holland, read 
before the British Association, Section C (Geology), Bristol, 
1898, printed in the January number of this Magazine, f on 
"The Comparative Actions of Subaerial and Submarine Agents 
♦Extracted from the Geological Magazine, Decade IV, Vol. VI, No. 
422, p. 354, August, iSgg. 
tGeol. Mag., January, i8qq, pp. 30-1. 
