Revieiu of Recent Geological Literature. 255 
Professor Willams' notes are the outcome of much labor in the field 
by many individuals, extending over more than a decade. 
Concerning the general problem presented, professor Williams says : 
"On account of the apparent conflict between the interpretation of the 
stratigraphy made by the field observers and the interpretation sug- 
gested by my study of the fossils, I went to Arkansas in August, 1890, 
and traversed the ground with Dr. Branner, confirming the fact of 
sudden and great change in the paleontological horizons, in several 
places where the lithological characters of the rocks and the strati- 
graphy little and often obscure evidence of facts. Although our ex- 
amination was rapid and very few additional fossils were accumulated, 
the great importance of the Devonian interval, as it may be called, was 
clearly established. The course traversed was from Batesville west- 
ward, across country, to Eureka Springs. The best expression of the 
details of the interval were seen at St. Joe, where, without apparent 
unconformity of strata, the Silurian limestone is separated by a few 
feet of green shale and nodular sandstone, called Sylamore sandstone, 
from the Carboniferous limestone." 
The geological formations are assigned ages as follows : 
Genevieve or Boston group. 
Batesville sandstone. 
Spring Creek black shales. 
Carboniferous. 
Cherty beds (Boone chert). 
Carrollton limestone. 
St. Joe marble. 
Eureka shale (typical). 
Devonian. 
Sylamore, sandstone. ' 
Eureka shale (in part). 
Silurian. St. Clair limestone. 
Ordovician. 
Polk Bayou limestone. 
Izard limestone. 
Saccharoidal sandstone. 
Calciferous, or Magnesian, limestone. 
The faunas of the several formations are then indicated and briefly 
discussed. Among the noteworthy features brought out, none is ot 
greater significance than the determination of the dual character of 
the great limestone which the Arkansas field geologists had long called 
the St. Clair limestone. One part carries a typical Ordovician fauna, 
while the other contains Silurian fossils. The distinction is es- 
pecially important from an economic standpoint. The manganese 
deposits of the state are found on the horizon which separates tlio 
two parts of this limestone, whenever the two are present in the 
same section. "Whenever the manganese is present it is always above 
or at the top of the Polk Bayou limestone of the section. The evi- 
dence is conclusive, therefore, that the erosion, causing the interval, 
was after the deposit of the Polk Bayou limestone, and the evidence 
of the few fossils in the Cason shale indicates that the manganese- 
