282 The American Geologist. ^^y, 1903. 
coal is a common feature of the loess near its base. Todd also 
frequently mentions, and sometimes illustrates in his figures, 
a stratum or several strata, of stratified silt near the bottom 
of the loess, such as, according to professor Salisbury, are ex- 
ceedingly rare at the bottom of the loess, and which are com- 
parable to4he silt layer at the base of the loess at the Concan- 
non farm. 
15. The Unio which was taken from the roof of the tunnel 
at the Concannon farm by professor Williston and Mr. Long 
was shown to the members of the party, and to the writer, at 
the time of its extraction. It has been stated that its valves 
were still united, but of that the writer knows nothing fur- 
ther than the statement of professor Chamberlin, p. 769. In 
case this Unio were a true fossil, it would be, of itself, suffi- 
cient proof of the subaqueous deposition of the materials in 
which it lay. Land shells may form fossils in aqueous depos- 
its, but never water shells in land deposits. It is, a priori, 
however, the strongest evidence of sub-aqueous origin of the 
loess in which it was found, and the agreement which it has 
with the obvious other features of the deposit serves to ac- 
cumulate such a weight of testimony in the same direction that 
it requires the greatest hardihood to attempt to explain it on 
the hypothesis of land origin of that deposit. 
16. The statement here made shows the needlessness of 
the "academic statement" concerning scour-and-fill, for this 
complete statement of theory makes no appeal to scour-and-fill. 
Indeed, it is evident, from the position of the tunnel as shown 
in fig. I (Prof. Chamberlin's fig. 13), that the Missouri river 
is shut off from access to the place of the skeleton by the 
Carboniferous blufif. It might reach it by back-set of water, if 
it were ever high enough, forming a bayou up the creek's val- 
ley, but the operation of scour-and-fiill is confined to the chan- 
nel of the river. 
As to the extent of the deposit, containing the skeleton — 
that is not determined by any facts yet brought to light. It 
appears to be the same deposit that covers the region. It as- 
cends the higher slopes, i.e., unless some distinction can be 
made to appear by future exploration, fills the ravines and 
gorges adjacent, and is not terraced or otherwise topograph- 
ically or areally set off as separate from the loess of the region. 
