270 The American Geologist. ^^^'' ^^°^- 
4. At this point it will be necessary to refer to the follow- 
ing diagram ; in which A represents the point at which the 
lowest rock appears in the creek bottom. At this place there 
is a little rapid spot and a good watering-place for horses. 
The rock exposed is the same stratum as forms the floor of the 
tunnel. B represents the most eastern point at which rock iu 
situ is seen in the south bank of the tributary creek. C and D 
are points situated in the creek valley directly eastward from 
A and B, but on a line coincident with the average line of the 
Missouri bluffs as they strike past the mouth of the tributary. 
E is the entrance to the Concannon tunnel. F is the entrance 
to the open tunnel. G is the cjuarry on the north side of the 
creek. H is the place of the skeleton. The plan is approxi- 
mately drawn to scale. 
As to the temporary nature of the creek, it is found, by 
following it up. that the valley extends about a mile westward, 
formed by three tributaries that drain about one square mile, 
and that it is wide and deep, but rarely showing rock, compar- 
able with its appearance at its mouth. Mr. Michael Concannon 
has stated in writing: ''In my memory, some thirty or more 
years, the creek has never been dry above A, while below that 
point it is dry every summer. Between the cellar and A there 
is no rock vissible, but the ledge that is in the creek bottom at 
A is the same that is in the floor of the cellar. The distance 
from A to C is five hundred and ten feet. The distance from 
B to D. is ninety-six feet. We have never discovered any rock 
in the north bank of the creek. The quarries on the north side 
are about seventy-five or eighty feet higher than the cave level, 
[and] near the top of the river bluff". Immediately east of the 
[entrance of the] tunnel the creek has excavated its bed twenty 
feet or more, while a little further east we had a well twenty- 
four feet deep and did not strike bedrock." Piles were driven 
thirty feet in the alluvium in the construction of the railroad 
bridge over the creek at its mouth. 
Here is a creek valley, therefore, which has been excavated 
in the rocky structure of the jMissouri river bluffs at least sev- 
enty-five or eight_v feet, from the quarries on the north bluffs 
down to the level of the floor of the tunnel at E. and thence 
(say) twelve feet to the level of the creek's flood-plain, and 
