Geology and Natural History. 61 
and the hard, unchanged rocks beneath were exposed and gla- 
ciated; since which time the chemical decomposition of the sur- 
face has been insignificant. 
porting an abundant vegetation), but little subject to the degrad- 
mg influences of atmospheric waters.— Boston Sve. Nat. Hist., 
Oct., 1873 
. 
published result, was inaugura in 1871, when a “ Mining, 
Metallurgical and Geological Bureau” for the State of Missouri 
and valuable account of the Pilot Knob and other iron regions 
of the State, and their products. It commences with a chapter 
ores and pig irons by A. A. Blair. seis follows a thorough dis- 
a of the distribution, modes of occurrence, and characters of 
€ iron ore-beds or deposits, by Dr. Schmidt. 
Prof. Pumpelly states in his report that the Archwan rocks of 
