i 
76 MEMOIRS OF THE CARNEGIE MUSEUM 
fragments of bones which are worn down to the shape of a pebble. These conditions 
could have been brought about in no other way than by the action of water in 
motion. There was here most likely a stream of considerable magnitude, instead 
of a lake, as was suggested by the writer (80, p. 49). The fossil-bearing bed has all 
the appearance of a stream the bottom of which was covered by quick-sands. In 
the quarry located on “ University Hill” (see fig. 28) there are distinct evidences 
of narrow and rather shallow channels, which were separated by sandbars of greater 
or lesser dimensions. The bone-layer of this quarry is thus, irregularly separated, 
although confined to one general level throughout portions of the base of the hill. 
It seems reasonable to suppose that in the immediate vicinity of the Agate 
Spring Fossil Quarries the ancient fauna of the region found a favorite crossing of 
this stream. The remains of the unfortunate animals which attempted to ford the 
river under unfavorable circumstances furnish the records which the collector is 
fortunate in securing, and which give a glimpse into the struggle for existence in 
those early times. 
In this connection it is interesting to note certain topographical features in the 
vicinity of the Agate Spring Fossil Quarries. In this region the general direction of 
the Niobrara River is east and west. Very often the side cafions of this stream ex- 
tend in a direction contrary to that which one would naturally expect. The draws 
and ecafions on the north side extend diagonally southeastward and in a perfectly 
natural direction towards the main stream, while very often the cafions on the south 
side extend diagonally northwestward or up-stream, which is generally regarded as 
a feature of stream piracy. This anomalous feature was quite perplexing to me for 
some time, and it was not until I had studied the character of the sediment in con- 
nection with the topography that any tangible explanation was reached. It is a 
well-known fact, which has been observed by Darton, Hatcher, Peterson, and others, 
that in these Miocene beds are masses of pipey concretions of greater or less extent, 
which always have their long axes directed in a nearly northwest-and-southeast 
direction. The cafions to the north of the Niobrara would have no difficulty in 
cutting their way through to the river in a natural course, while those on the south 
side of the stream would sometimes have to accommodate themselves to the up- 
stream direction which is the course of the least resistance to the erosive elements. 
In this way there are developed sharp ridges and hogbacks, nearly always in the north- 
west and southeasterly direction on either side of the river. Chimney-rocks and 
pillars of numerous shapes are seen along the course of the Niobrara River for some 
forty miles in this general locality. 
The entire Miocene section, and especially the lower Harrison beds, are appa- 
