486 STUART WELLER 
Nevada. Ambocoeliaumbonata,a single individual of which has been 
observed, is a common Hamilton species in New York, although 
a variety of the same species also occurs in the Upper Devonian. 
Orbiculoidea newberryt, also represented by a single observed 
specimen, has been recognized only in the Waverly series of 
Ohio, near the base of the Carboniferous. 
The presence of Ptyctodus is certainly indicative of the Devo- 
nian age of the fauna, but Dzplodus has previously been recog- 
nized only in Carboniferous strata, and the presence of two 
species of this genus with the Waverly species of Orbiculoidea 
would seem to indicate a very late Devonian age. 
The presence of a fauna of this age in such a situation, is of 
extreme interest. Thenearest point where Devonian strata form 
the surface rock is probably in northwestern Indiana, but that 
region is so heavily drift covered, and has been so. little studied, 
that the exact distance from Elmhurst to the nearest Devonian 
strata in that direction cannot be determined with accuracy. 
Furthermore, the Devonian strata known in northern Indiana, 
are the black shales, and do not contain a fauna with Ptyctodus. 
The nearest actual outcrop of Devonian is at Milwaukee, Wis., 
eighty miles north of Elmhurst; and the nearest outcrop to the 
west is near Rock Island, Ill., one hundred and thirty miles 
away. At both of these localities Ptyctodus calceolus occurs, but 
the strata are believed to be somewhat older than the material 
from Elmhurst. 
The presence of this Upper Devonian fauna at Elmhurst, bur- 
ied as it is deep down in the Niagara limestone, indicates with 
certainty that during the greater part of Devonian time, the 
region now known as northern Illinois was above sea level. It 
was part of what was probably a large land surface, stretching from 
the Wisconsin land on the north to the Ozark land of Missouri 
on the south. The waters which collected upon this land sur- 
face in part percolated through the underlying rock strata and by 
solution increased the size of many joint cracks. Ata later per- 
iod, near the close of the Devonian, when the sea again occupied 
the region, sand was sifted down into these open joints, and with 
