236 The American Geologist. October, 1905 
extensive enough to form any definite conclusion, it would 
seem that possibly a large stream flowed to the Gulf along 
the line of the sand deposits, the deposits being the debris 
left by its ever changing channel. A re-elevation of the 
central plain, after a long lapse of time, diverted the drain- 
age and left the region, first, a ponded area as is, shown by 
the pond-holes, and, then, arid land. 
Again, the origin of the deposits might be explained by 
another hypothesis as follows : That after the re-elevation 
of the Rocky mountains just before or at the beginning of 
the Loup Fork epoch, the streams, flowing east from the 
continental divide, had not, as yet, formed permanent chan- 
nels across what is now our western plains. Consequently, 
after flowing rapidly down the mountain slopes, they 
spread out on reaching the slack-water region of the plains 
forming dry deltas or alluvial-fan deposits. This they con- 
tinued to do till time and re-elevation of the plains region 
caused them to cut permanent channels to the Mississippi 
river and the gulf of Mexico. 
The Ogallala {?) formation was found exposed in a cut 
on the Rosebud-Boarding School wagon road one-half mile 
northeast of Rosebud. In general appearance and in com- 
position it resembles the "mortar beds" of Kansas very 
much. It is essentially a limestone of the calcareous mag- 
nesian type containing many impurities. The limestone is 
wavy, looks much as if it had been run through a crimping 
machine before hardening, is somewhat continuous in stra- 
tum form, and, besides being gritty itself, is intermixed with 
grit and sand. 
In this formation the writer found bones of the masto- 
don, horse and camel, fragments of turtle shell, and the 
bones of birds. 
In places the limestone of these beds is used for build- 
ing purposes, for which it is said to be a good rock. 
On the map (plate XII.) these beds and the underlying 
Arikaree are mapped together as Loup Fork Tertiary. 
Glacial (?) debris, rock, which seemed to be of glacial 
origin, was noticed at several places on the bluffs of lower 
Oak creek. As the great glacier extended to the Missouri 
adjacent, it is highly probable that a glacial lobe crossed 
