104 Wisconsin Academy of Sciences, Arts, and Letters, 
sheet of its formation which owes its preservation to collapse of the 
roof of an Eopaleozoic cavern seemed to fit the case. 
The Oneota is of Upper Ozarkian age. The sea of its epoch 
lasted a long time in the southern Appalachian region but finally 
spread very widely over southeastern North America. Its rocks 
and characteristic fossils are recognized also in Missouri (Gas¬ 
conade formation), in Alabama and east Tennessee (Chepultepec 
formation), in Pennsylvania, and in eastern New York. At the 
close of its stage this great inland sea was withdrawn perhaps en¬ 
tirely. The next succeeding invasion laid down the limestone and 
graptolitic shale deposits with which the accessible record of the 
history of the Canadian period begins. Whereas the preceding 
Oneota-Gasconade-Chepultepec stage spread northeastwardly from 
the south and west, the succeeding Lower Canadian stage had its 
development in North America mainly or entirely in Pennsylvania 
and New York. Judging from the distribution of its deposits this 
new sea must have differed from the preceding also in the location 
of its inlet and the direction of its invasion. It came in from the 
Atlantic side of the continent, whereas the preceding late Ozarkian 
sea invaded from the south. Evidently then the physical changes 
that occurred in passing from the Ozarkian to the Canadian period 
involved very considerable local warping and also more generally 
effective differential vertical movements of the lithosphere. The 
geographic changes at this time—meaning particularly changes in 
arrangement and outlining of water and land areas—also the 
faunal modifications, were greater and more important than at any 
other time between the close of the Cambrian and the beginning of 
the Ordovician period. 
The Ozarkian-Cambrian break .—To get a true conception of the 
diastrophic changes that' occurred in America during the passage 
from the Cambrian to the Ozarkian period we must study the 
stratigraphic records preserved in the great Appalachian and 
Cordilleran geosynclines. However, as we found in discussing the 
younger Paleozoic breaks, the record in Wisconsin and adjoining 
States regarding the Ozarkian-Cambrian break also is far from 
blank. In fact, the Devils Lake sandstone, which is the oldest of 
the Ozarkian formations in Wisconsin, affords a more impressive 
development and display of conglomerate than has . been observed 
at this horizon anywhere else in America. This sandstone attains 
a thickness of at least 100 feet and at' many places includes—as in 
Parfrey Glen, east of Baraboo, and at the northern end of the 
