Fauna of the Morroiv Group 
65 
Schuchert/^ in 1910, ascribed an early Pottsville age to the 
Morrow fauna which is stated to be largely new. Similarities 
are noted between it and the fauna listed by Meek from ‘‘Old 
Baldy” near Virginia City, Montana, which “in the light of the 
Arkansas collections . . . must now be referred to the Potts- 
viilian.'’ 
Ulriches concurs in the reference of the Morrow to the early 
Pottsville. He states also that the Caney shale, of the Ouachita 
geosyncline, “is in part represented by the upper black shale of 
the Morrow group in northern Arkansas.’' 
In the Index to the Stratigraphy of North America, Bailey 
Willis^^^ gives a brief review of the literature concerning the 
Morrow formations and in his correlation table places the group 
at the base of the Pennsylvanian series. 
The Morrow Fauna 
From the material upon which these studies are based 158 
species have been identified and are discussed in the following 
pages. Seventy-nine of these are here described for the first 
time; twenty-two others have been referred to genera, six of 
them questionably, but on account of their fragmentary condi- 
tion or poor preservation have not been given specific names 
though most of them probably represent undescribed forms. 
The fauna is composed of the following forms of animal life: 
corals, 9 genera and 11 species; blastoids, 1 genus and 2 species; 
crinoids, 5 genera and 7 species; echinoids, 1 genus and 1 spe- 
cies ; bryozoans, 15 genera and 38 species ; brachiopods, 20 genera 
and 48 species ; pelecypods, 16 genera and 29 species ; gastropods, 
12 genera and 14 species; cephalopods, 2 genera and 4 species; 
trilobites, 1 genus and 2 species; fishes, 2 genera and 2 species. 
The complete faunal list is presented in Table I. 
Faunal Horizons 
In the eastern part of the Morrow basin, corresponding 
roughly to the portion east of the Arkansas-Oklahoma boundary, 
three distinct horizons of fossiliferous limestones have been rec- 
ognized. These are separated by variable, but in most places 
not great, thicknesses of non-fossiliferous sandstones and shales, 
the interval between the upper two of the three also including 
a thin seam of coal. The question of the similarity or difference 
