THE CAMBRO-SILURIAN QUESTION IN MISSOURI 
AND ARKANSAS. 
Ir is a remarkable fact that of all the great Mississippi basin 
with its area equal to more than one-third of that of the whole 
United States, its very center, the portion which is richest and 
most important of all in mineral wealth, should be the only por- 
tion which has remained geologically a veritable terra incognita. 
The region is widely known as the Ozark uplift, a broad dome 
which occupies the southern half of Missouri and the northern part 
of Arkansas. The rocks composing it form an important sequence 
of dolomitic and arenaceous beds which are known to lie between 
the horizon of the Trenton limestone and the crystalline, or 
Archean, complex; and which have recently been termed by 
Broadhead? the Ozark series. 
In the earlier geological reportsof Missouri great prominence 
was given to the succession of magnesian beds. By Swallow? there 
were considered to be four thick limestones, separated by sand- 
stones. They were known as the First Magnesian limestone, at 
top, the First or Saccharoidal sandstone, Second limestone, and 
so onto the Fourth Magnesian limestone at the bottom. The 
aggregate thickness of this ‘“Magnesian Limestone” series was 
considered to be over 1200 feet. It was referred to the Calci- 
ferous division of the New York section as then understood. 
Since the appearance of Swallow’s report other work has been 
done in the region, and of recent years interest in the subject 
has been revived. In southeastern Missouri more attention has 
been directed to the Magnesian rocks than perhaps anywhere 
else in the Ozark uplift, and although many new facts have been 
obtained much additional information is necessary before satis- 
t American Geologist, Vol. VIII, p. 33. Minneapolis, 1891. 
?Geol. Sur. Missouri, tst and 2d Ann. Repts., p. 60. Jefferson City, 1855. 
519 
