History of the Missouri Paleozoic. — Broadhead. 383 
to the Rocky mountains beyond. In southern Illinois the 
general surface is hut little over 500 feet, reaching 700 and 
■800 feet in the central portion. Borings at the Insane Asy- 
lum, St. Louis, would indicate that the Archaean lies about 
3,800 feet below the surface, or about 3,200 feet below the 
sea level. Not altogether reliable records of a Jackson county 
boring assert that granite was reached there about 2,500 feet 
below the surface, or 1,500 to 1,700 below the sea level. From 
■observed outcrops in central and southwestern Missouri we 
would suppose that borings in Nodaway county might pene- 
trate through 4,000 feet of strata to reach the Archaean, find- 
ing it about 2,800 feet below the sea. That would nearly 
agree with the measured depth at St. Louis. The Archaean 
floor in southern Illinois probably occupies about the same po- 
sition below the sea that it does at St. Louis. At the close of 
Archaean time the state would be occupied by a deep sea, the 
Cambrian sea, through which in southeastern Missouri cer- 
tain granite and porphyry peaks protruded 500 to 1,000 feet 
above the waters; these are now seen in St. Francois, Madison, 
Iron, Reynolds and Wayne counties. Southeastern Missouri 
was probably dry land in the early Cambrian, but in the later 
Cambrian or early Potsdam period the Ozarks were occupied 
by a shallow sea whose waves dashed furiously against the 
Archaean hills, sufficient to erode enough material to form a 
sandstone. This sandstone is found upon a limited area in 
about four counties of southeastern Missouri. It is generally 
of coarse texture and includes pebbles of the Archaean. Else- 
where the strata are covered with more recent deposits. Most 
of the Archaean area subsided to a depth of 2,000 to 3,000 
feet in order to receive the Lower Magnesia n limestone and 
interbedded sandstones of the Mississippi valley, extending 
from central Texas to lake Superior; only certain peaks in 
Llano and Burnet counties, Texas, and in six or seven coun- 
ties of southeastern Missouri were exposed. 
The life of this earty Cambrian sea was limited in number 
of species. In Missouri it embraced a few Orthocerata, a 
Lituites, a small Orthis, a Pleurotomaria, a Maclurea, an Oph- 
ileta, two or three species of Straparollus, probably two spe- 
cies of Murchisonia, and three or four species of trilobites; 
while in the Potsdam of Wisconsin and .Minnesota several 
