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IOWA ACADEMY OP SCIENCE 
end of the excavation west of the track is reported coarser than 
that from the east end of the excavation, which end is farther 
away from the edge of the upland. 
FOSSILS. 
In the old gravel pit east of the Chicago, Eock Island and Pa- 
cific railroad at Avon a tusk and several large bones thought 
to be of a mastodon or an elephant are reported by one who saw 
them. Several other bones found there later are now in the col- 
lection at Simpson College. These last specimens were studied 
by Professor Oliver P. Hay of ’Washington in 1914: with the fol- 
lowing result : ‘ ' The metapodial and astragalus belong to Bison. 
The piece of lower jaw and the vertebra are those of a caribou 
(Rangifer). The tooth is one of Rangifer muscatinensis. The 
atlas is that of a musk-ox {Symhos cavifrons) 
I had previously expressed to Professor Hay my doubt as 
to whether the lowest portion of the gravel was really Aftonian 
in age of deposition, and my reasons for that doubt. After iden- 
tifying the specimens he wrote, ‘ ‘ It seems to me you are right 
in doubting the Aftonian age of those gravel beds. They are 
probably Wisconsin or early post-Wisconsin.” Later he adds 
that the bones of the reindeer and musk-ox indicate an ice age, 
though it ‘ ‘ might be later with these bones washed out of a glacial 
deposit. ’ 
SUMMARY. 
1. The gravels are in a low terrace along the southern margin 
i>f the Wisconsin drift and even extending into valleys in the 
Wisconsin drift area. 
2. From the area above described a low terrace is found 
along the Hes Moines river to the Mississippi. Northward along 
the Mississippi river a terrace is conspicuous to within the area 
of Wisconsin drift in Wisconsin, where the terrace is referred 
to the fiooded condition of the streams at the melting of the Wis- 
consin ice sheet. 
3. The fossils are not pre-Wisconsin ; they are Wisconsin in 
age, or derived from Wisconsin drift. The gravel itself con- 
tains an evidence of the presence of ice. 
CONCLUSION. 
It therefore appears that the sand and gravel in the river 
valleys and forming a low terrace at Valley Junction, Has 
Moines, Avon and Carlisle (and elsewhere in this part of the 
state) were laid down in the closing stages of the Wisconsin ice 
age. The surface of the terrace has since been modified both 
by erosion and by deposition. 
Department of Geology, 
Simpson College. 
^Published with Professor Hay’s consent. 
