THE AGE OF THE MAMMALIAN FOSSIL FAUNA 513 
fragment of a jawbone with teeth was found attached to a con- 
cretion when the overlying clay was being washed away by the 
hydraulic method. Unfortunately, the specimen was not saved. 
‘The concretions range in size commonly from 1 inch or less to 
5 and 6 inches in their longest diameter. Some include Polygyra 
shells, characteristic of the lower loess from bottom to top, while 
others contain pebbles of the underlying drift. A large per- 
centage of each concretion appears to be of very fine material, 
which has given them the name of “loess nodules,” although they 
do not occur strictly in the loess. They are secondary, younger 
than both drift and loess, their content of lime having been dis- 
solved from the overlying formations which, together with the 
finely divided material of the loess carried probably in the colloidal 
state, has been deposited in concretionary form in the contact 
zone between the loess and the drift. In the forming of some of 
these concretions some of the pebbles in this zone were included, 
and, in some instances, mammalian remains. 
Composition of the fauna and its age.—The following is a list 
of species which have been identified by Dr. rae in the McAdams 
collection: 
Megalonyx oe cones ‘Extinct ground sloth 
Equus sp. indet. Extinct horse 
Platygonus cumberlandensis ? Extinct peccary 
Sangamona fugitiva Large extinct deer 
Cervales roosevelt ? Extinct moose 
Rangifer muscatinensis ? Extinct reindeer 
Taurotragus americanus Extinct American eland 
Symbos promptus )xtinct musk ox 
Mamut americanum Extinct mastodon 
Castor canadensis Canadian beaver 
Castoroides ohionensis Extinct giant beaver 
Marmota monax Ground hog 
Geomys bursarius Pouched gopher 
Ursus americanus Brown bear 
The quarry from which most of the remains were secured 
shows a gentle depression at the top of the limestone, as if the sur- 
face of the limestone led to a sink, such as characterizes the karst 
topography of the upland directly back from the quarries. An 
examination of two of these sinks revealed their origin to be joint 
1 Personal communication. 
