906 THE JOURNAL OF GEOLOGY. 
Wisconsin and the northern portion of Illinois, rocks of much 
younger age lie upon the Silurian beds, indicating that during a 
long period between Silurian and Carboniferous time this penin- 
sula extended far to the south. The Ozark Silurian or Ordo- 
vician region has also lying upon its flanks rocks of much 
younger age, indicating that during the greater part of Devonian 
time it was a body of dry land of more than the present extent 
of the older rocks. There seems to be good reason, therefore, 
to suppose that during this period the Wisconsin peninsula and 
the Ozark Island were joined. This, however, would not alone 
form a sufficient barrier to separate the two faunas, as they 
could easily migrate around the southern end of this pen- 
insula. There are, however, small patches of Silurian rocks 
exposed in Arkansas, Indian Territory and Texas, and all of these 
are surrounded in a similar way by rocks of much younger age, 
and this suggests the probable extension of this land barrier far 
to) the "southwest. ) Furthermore, athe mpresencessinmmuiemedsr 
American Devonian fauna of representatives from the South 
American province necessitates a shore line along which the 
migration could have taken place. This suggests the extension 
of this land into South America. With the existence of such a 
land tract the separation of the two Devonian faunas would be 
effectual. 
If the conclusions of the last paragraph are correct, the 
Ozark region was not an island during earlier Devonian time, 
but was included in a long peninsular extension of the ancient 
northeastern land, or more probably in an isthmus joining it to 
some larger body lying to the southwest. By a partial sub- 
mergence of this peninsula or isthmus the Ozark Island was 
formed. The depression of this land area was neither sudden 
nor continuous, but the movements were oscillatory in their nature. 
Union of eastern and western Devonian provinces —The earliest 
evidence of the union of the two seas on either side of this 
narrow strip of land is found in the appearance of an entirely 
foreign fauna in the midst of the Hamilton beds of New York. 
This-is-the-Guboides fauna of the Tully Limestone. - From a 
