144 The American Geologist. September. 1903. 
These facts show that either there is no Onondaga in Wiscon- 
sin, Iowa and Missouri, or that the equivalent faunas found 
in these states were separated from the eastern area by a 
nearly completely effective barrier preventing intermigration. 
'1 he former hypothesis is believed to be the truth as will be 
seen later. 
The corals of the Hamilton of New York, western Ontario, 
and Louisville are also harmonious and belong to one province. 
Of the 34 widely dispersed species found about Thedford, On- 
tario, 11 occur in New York, about 15 at Louisville, and the 
same number at Thunder Bay. The Hamilton of this area 
received many of its species from the Onondaga below, and 
the coral faunas of these two formations belong to one prov- 
ince and form an evolutionary series. 
Comparing this eastern area with that of Traverse Bay, 
Michigan, Milwaukee, Wisconsin, Iowa and Missouri, a very 
marked dissimilarity is noted. Of the 34 widely dispersed 
species of Thedford, which is the westernmost locality of the 
eastern area having a typical Hamilton fauna, but 7 are 
found at any one place in the western area mentioned above. 
These are 1, Acervularia davidsoni, 2, A. profunda, 3, Aulo- 
pora serpens, 4, Favosites alpenensis, 5, F. digitatus, 6, F. pla- 
centa, and 7, Heliophylluni juvenis. Two of these, numbers 
3 and 6, have a world wide distribution, while only one, F. 
placenta, occurs in New York. Out of a total of 106 widely 
dispersed Middle Devonic corals, but 24 occur in western 
Michigan, Wisconsin and Iowa. Of these 24 species, but 6 
occur in New York, the other 18 not passing beyond the west- 
ern half of the eastern province. 
Stromatoporoids are not rare in the eastern province but 
are more prominent along the western side of this area and 
particularly about Alpena, Michigan. In the western province 
they are far more prominent, and this is especially true for the 
Petosky region. Not only this, there are also species in the 
western area not seen in the eastern. 
The brachiopods along the northern side of the eastern 
province are harmonious from central New York southwest- 
ward to Columbus, Ohio, and westward to Thedford, but grow 
less so toward Thunder Bay, Michigan. While the last named 
region has a noticeable blending of species of both the eastern 
