224 “The American Naturalist. [March, 
relation table accompanying the descriptions. (Proceeds. Amer. Philos. 
Soc., XX XV, 1896.) 
The Lead and Zinc of Iowa.—In a report on the Lead and 
Zine Deposits of Iowa, Mr. A. G. Leonard states that these ores occur 
in crevices in the Galena limestone in the northeastern part of the State, 
in what is known as the driftless area. Contrary to the general rule, 
that ore deposits are found with areas of disturbance in the earth’s 
crust, the ore deposits of the upper Mississippi are found in strata which 
show no evidences of having been subjected to dynamic forces. The 
author accepts Chamberlain’s theory as to the localization of these ores, 
viz., currents of the old Silurian sea. The oceanic waters impregnated 
with metallic salts derived from the leaching of the adjacent lands 
were borne by currents to areas where there was an abundance of organic 
life, and here the metals would be extracted and thrown down along 
with the sediments. As to the filling of the crevices, he adopts the 
lateral secretion theory, as being more in accord with his observations. 
(Iowa Geol. Surv., Vol. VI, 1896.) 
The Eruptive History of the Yellowstone Park.—Mr. Hague 
collates a series of facts to demonstrate that the pouring out of igneous 
rocks in the Yellowstone Park began with the post-Laramie uplift, or 
closely followed it, the outflow continuing with greater or less energy 
throughout Tertiary time. The great value of paleobotany as an aid . 
in determining the age of geological formations is illustrated in this 
region. At least five distinct and important geological periods are de- 
fined by their fossil flora, of which four are exposed in the park within 
a few miles of each other. 
The following table shows the relationships between the different 
geological formations and the floras which characterize them: 
Formations. Flora. Age. 
ESEE E 
Basic breccia Tamar Upper Miocene. 
Intermediate breccias....... Intermediate Fbora.......... Lower Miocene. 
Acid DPOCOER, .o<ccsesdisece, sis Fort Unions esses sociva sison ene. 
Agglomerates, Waterlain I ivingstone Cretaceous 
Igneous Material. 
Sandstone Laramie Cretaceous. 
Bt ee 
(Amer. Journ. Science, 1896.) 
