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POPULAR SCIENCE REVIEW. 
atmospheric denudation, and the gradual removal of the soluble constituents 
has left important residuary deposits of such substances as were insoluble, 
especially in the Silurian strata — as clay, flint, &c. The more conspicuous 
instances of this kind among the pre-Silurian rocks are residuary occurrences 
of iron ore ; the instance of Iron Mountain is an extreme case, where the 
decomposition of the porphyry in mass facilitated the separation of the ore 
from the rock and the mechanical removal of the. latter. 
Although Missouri is one of the richest States of North America in iron 
ores, they are very unequally distributed. By far the richest portion of the 
State is in the greater part of the counties situated between the Mississippi 
in the east and the Upper Osage river in the west, so that according to 
present knowledge there are three principal and important iron regions in 
Missouri. (1) The eastern region, composed of the south-eastern limonite 
district and the Iron Mountain specular ore district. (2) The central region, 
containing principally specular ores, having its outlet over the St. Louis 
and the Atlantic and Pacific railroads. (3) The western, or Osage region, 
with its limonites and red hematites ; the upper Osage district also contains 
good deposits of subcarboniferous red hematites, occurring in the same way as 
in Callaway county. The mode of occurrence of the iron ores is variable ; 
they are found either as deposits of specular ore in porphyry and sandstone, 
as disturbed and drifted deposits of the same ore, as strata of, or as disturbed 
and drifted deposits of, [red hematite, or as deposits of limonite on limestone, 
or as drifted deposits of the same ore. 
The coal-measures of Missouri comprise an area of nearly 23,000 square 
miles, of which the largest portion occurs in the north-west and west 
districts, with about 160 square miles in St. Louis, and a few outliers in 
Lincoln and Warren counties. They are divided into the upper, or barren 
measures, the middle and lower measures, the larger exposed portion, more 
than one-half, belonging to the last division, and which are the richest in 
coal. The thickness of the Missouri coal-measures is about 2,000 feet, with 
a total aggregate of 24 ft. 6 in. of coal ; the lower measures, about 300 feet 
thick, contain five workable seams, in all 13 ft. 6 in. of coal ; the middle, 
about 300 feet thick, with seven feet of coal, including two workable seams 
of about two feet each, and the upper measures, with a thickness of 1,300 
feet, contain only four feet of coal made up of thin seams. The coal seams 
are intercalated with a rich carboniferous marine fauna, of which a list is 
given at the end of the volumes. 
GEOLOGICAL SURVEY OF THE STATE OF MISSOURI* 
T HESE reports scarcely represent the present knowledge of the geology of 
this State, as they appear to have been prepared some time since, and 
remained unpublished. The maps were engraved, and the impressions contained 
* “ Reports of the Geological Survey of the State of Missouri, 1855-71.” 
By G. C. Broadhead, F. B. Meek, and B. F. Shumard. Jefferson City : 
1873. 
