:;.s-J The American Geologist. December, 1894 
recognized over 600 feet of Upper Silurian in that count}'. 
Northwardly it becomes thinner, not being observed at all in 
St. Louis, St. Charles and Jefferson counties, but may be 100 
feet thick in Pike county. In Montgomery county about 20 
feet of gray limestone may be referred to the Upper Silurian, 
and this is restricted to a small area in Montgomery and Cal- 
laway counties. Certain terranes being wanting in central 
and southwestern Missouri the Paleozoic rocks, in their areal 
distribution, would have much less average thickness than the 
section above gives. 
In southwest Missouri the group between the St. Louis and 
Chouteau cannot well be separated. To such Prof. H. S. 
Williams has appropriately given the name "Osage series." 
The Ozarks belong to Missouri and in part to Arkansas. 
The Boston mountains are of another system, extending west- 
wardly into the Indian territory. Farther south is the Wash- 
ita system, extending from Little Rock west to the western 
part of the Indian territory. The area of Missouri, according 
to the census of 1890, is 69,415 square miles. Most of south- 
ern Missouri is included in the Ozark plateau, an elevated 
tract which in Missouri contains about 36,000 square miles; 
and its total area is probably 50,000 square miles, including 
part of Arkansas. This plateau is limited on the east by the 
Mississippi ; on the north by the Missouri and Osage rivers ; and 
on the west by a line about 30 miles east of the western state 
line. The Arkansas river may be the southern limit. The 
eastern portion of north Missouri is elevated about 700 feet 
above the sea ; passing westwardly it rises by gentle undula- 
tions to 1,100 and 1,200 feet in the northwest. The Ozark 
plateau near its eastern border is 700 to 800 feet above the 
sea, but within 30 miles it rises to 1,200 and 1,500 feet. The 
porphyry peaks of southeastern Missouri rise 1,200 to 1,800 
feet above the sea, while the unaltered sedimentary rocks sur- 
rounding them rest unconformably upon them at an elevation 
of 1,100 to 1,200 feet above the sea. Passing westwardly they 
rise to 1,500 feet in Webster county, 1,700 in Wright, 1,350 in 
Green, 1,530 in Barry county, and nearly 2,000 feet in the 
Boston mountains of northwestern Arkansas. Along the 
western state line the elevation is 850 to 1,100 feet, while be- 
yond in Kansas the country gradually rises to the plains and 
