Geological History of the Ozark Uplift — Broaclhead. 7 
may include about 36,000 square miles within the state of 
Missouri, and is chiefly limited on the east by the Mississippi 
river and a line not very far west of that river, but excluding 
the most of St. Louis county and 3,000 square miles of the 
swamp district in the south-east. Its western limit is an approx¬ 
imate line passing south-west from Glasgow, via Marshall and 
Sedalia, thence near the line of the M. K. & T. R. R. to the Osage 
river, thence southwardly to Stockton, and south-westwardly to 
and beyond McDonald county. Its southern boundary is not 
far from the Arkansas river. 
The Ozark plateau, near its eastern line, is 700 to 800 feet 
above the sea, and about the sanie elevation on the highlands 
near its northern line. The Archaean peaks of south-east 
Missouri rise 1,200 to 1,500 feet above the sea, while the un¬ 
altered sedimentary rocks surrounding them are but little over 
a 1,000 feet above the sea, increasing in elevation as we pass 
westward, until in Webster county they are 1,500 feet, in Wright 
county 1,700 feet and in Barry county over 1,500 feet above 
the sea. 4 little further west along the state line the elevation 
is 800 to 1,050 feet, reaching to over 1,100 feet in north-west 
Missouri, and in the south-west increasing still more in the 
direction of the Boston mountains. 
A little beyond the western line of Missouri there begins a 
rise gradually increasing as we pass westward across Kansas, 
while on the east just across the Mississippi the general surface 
maintains a nearly uniform elevation but very little over 500 
feet above the sea in southern Illinois. 
The rock structure of this plateau includes the Magnesian 
limestone series of the Missouri geological survey, the equiva¬ 
lent of the calciferous sandrock of the New York system, or 
the Upper Cambrian as defined by C. D. Walcott. 
Dr. Shumard’s measurements have given: 
Pulaski. Phelps. Franklin. 
First Saccharoidal sandstone, .. 30 ft. 175 ft. 
Second Magnesian limestone,. .... 150 ft. 300 ft. 
Second sandstone,.... 100 ft. 150 ft. 140 ft. 
Third Magnesian limestone,... 600 ft. 180 ft. 300 ft. 
Prof. Swallow recognized 50 feet of sandstone on the Osage 
below the Third Magnesian limestone with 300 feet of a Fourth 
Magnesian limestone still below. In Madison county I have 
