LOGAN. | The Upper Cretaceous. 2) 
upper horizon. Herein, undoubtedly, lies the explanation of the 
origin of the gravel beds. By the disintegration of the shale, and 
the dissolving of the limestone, the gravels accumuiated along the 
bed of the stream. Subsequently the stream changed its course, 
and the detritus from the bluffs filled up the old bed of the stream. 
After cutting down to a lower level the stream again changed its 
course, and exposing the old gravel beds which had, in the mean- 
time, been cemented into firm rock. 
THE NIOBRARA. 
Septaria.—'The Niobrara group occupies a narrow belt along the 
border of the Tertiary area and overlies the Benton. Its total thick- 
ness is between 350 and 400 feet. Lithologically it has been divided 
into two groups: the lower, or Fort Hayes limestone; and the 
upper, or Pteranodon! beds, or Smoky Hill chalk. 
Resting upon, and often embedded in the black shales of the 
upper Benton horizon, is a layer of shale containing many calcareous 
coneretiens to which the name Septaria has been given. It marksthe 
dividing line between the Benton and Niobrara. This zone.reaches 
entirely across the Benton-Niobrara area from Jewell county almost 
to the Arkansas river. The nodules are usually in the shape of 
flattened spheres, and their surfaces are either smooth or seamed. 
Some of them are solid, others. are hollow, and the cavity lined 
with a crystailine substance, usually calcite. The calcite crystals 
vary in color, from a dark wine color to transparent. At the base 
of Williams’ Butte, in Mitchell county, a field more than ten acres in 
extent is covered with the concretions, some of which are more than 
four feet in diameter. Many tons of them have been hauled away 
for museum specimens, or lawn ornaments. Some fine specimens 
of ammonites and scaphites have been found in them. Testudinates 
have also been found in that horizon. 
Fort Hays Limestone-—The Fort Hays limestone forms a continuous 
line along the bluffs of the Smoky Hill river, from the mouth of 
Hackberry creek to the western line of Ellis county. Here it dis- 
1 Since Pteranodon has been shown to be synonymous with Ornithostoma, some 
think the latter name should be used. 
