62 
Kirtley F. Mather 
Winslow formation, unconformity. 
^ j' Kessler limestone lentil, 0-30 
I Bloyd shale, 100-220 ft. j ft., near top. Coal seam, 
Morrow | black carboniferous shale.. ) inches. 
group J j Brentwood limestone lentil, 
I ^ 10-50 ft,, near base. 
1 Hale formation, 100-200 ft. Sandstone and shale with thin, 
1^ local, limestone lenses. 
Unconformity. Pitkin limestone. Fayetteville shale. 
Resume of Literature Concerning the Morrow Group 
The first geological description of the strata under considera- 
tion seems to have been that of David Dale Owen in 1858.^ 
He applied the terms “Archimedes limestone'’ to the Pitkin 
and “Millstone Grit" to the Winslow formations and described 
the coal seam of the Bloyd shale at various outcrops. 
Two years later, accompanying Owen’s second report, Les- 
quereux^ published descriptions of the fossil flora which he 
had collected from the Morrow coal horizon and commented 
on its similarity to the flora from the coals above the Millstone 
Grit. He therefore included the shales of the Morrow in the 
“Arkansas Coal Measures.’’ 
A more detailed examination of the Morrow formations is 
recorded in the description of the Geology of Washington 
County by F. W. Simonds,^ published in 1891. Here these for- 
mations are included with the Archimedes limestone and the 
Marshall shale [= upper part of Fayetteville shale] in the Boston 
group which is referred to the Chester, St. Louis, and Warsaw 
stages of the Lower Carboniferous or Mississippian series. 
The Hale formation is known as the Washington shale and 
sandstone, the Brentwood as the Pentremital limestone, and 
the Bloyd is called the Coal-bearing shale. Detailed descrip- 
tions of the numerous outcrops of these strata in Washington 
County are given. 
In 1895, David White^ stated that the flora of the “coal- 
bearing shale of Washington County, Arkansas, is largely iden- 
tical with and clearly belonging to the Sewanee group of Ten- 
nessee.’’ This reference of the Bloyd to the Pottsville stage 
seems to have been overlooked for, three years later, Drake^ 
followed the classification of the Boston group used by Simonds 
in 1891 and mapped the Morrow formations with his “Lower 
