384 The American Geologist. December, 1894 
other species of trilobites have been found. Sea worms 
abounded where the waters were more shallow, and left their 
tracks in irregular winding holes in the off-shore sandstone. 
In the upper beds sea weeds abounded, as shown by the lime- 
stones now exposed. Certain beds of the Second Magnesian 
limestone are largely made up of the accumulated mass of 
sea weeds bundled and pressed together, their form only pre- 
served, filled with calcareous matter. 
There were occasionally elevations long enough continued 
for sands to accumulate off-shore to become in later time beds 
of sandstone, then a sinking and accumulation of sediment in 
the deeper seas, until finally 2,000 feet had .been formed. 
Ages rolled on, the ocean beds rose, the granite and porphyry 
hills of southeastern Missouri, as well as those of Wisconsin 
and Minnesota, were eroded of their material during the vio- 
lent agitation of the waters near the close of the period of the 
Upper Cambrian. These sands were deposited around the 
sea's margin in remarkably clear water. The First sandstone, 
or the St. Peter's, was formed thicker along the Mississippi 
trough, or what was afterward the Mississippi trough, extend- 
ing from southeastern Missouri to St. Paul in Minnesota. East 
and west of that line the deposit is thinner, apparently en- 
tirely thinning out in Missouri at 100 miles west. 
After the laying down of this sandstone most of theOzarks 
were raised above water. Much of the upper strata were 
eroded and redeposited to form the rocks of later ages. The 
evidence is that after the Upper Cambrian period most of the 
Ozarks were elevated above the waters and have so remained. 
The Ozark series northward and eastward was depressed not 
less than 1,500 feet, and the Ozarks were separated from the 
Wisconsin highlands by a deep sea : this was the Silurian sea, 
and in it were laid down the Trenton and Hudson River beds 
toward the north and east. But this condition prevailed only 
as far west as Callaway county. From this we infer that the 
Ozarks at that time extended over the western and north- 
western part of Missouri. After the Lower Silurian was 
formed the western half of Missouri was dry land, but the 
country from Cape Girardeau to Ralls county was so de- 
pressed as to receive from 100 to 200 feet of sediment to form 
the Upper Silurian. Eastwardly the bottom gradually settled 
