318 EDWARD M. KINDLE 
uneven one, frequently rising or sagging on the north side of the 
river, as shown by the sketch (Fig. 7), but without indicating 
discordance of dip. On the opposite side of the river the Niagara 
dips from 6 to 18 degrees to the east, while the Devonian limestone 
lies horizontal above it, thus indicating deformation as well as 
erosion previous to the Jeffersonville submergence and showing the 
relationship of clino-unconformity. The photograph (Fig. 8) 
indicates this discordance in the dip of the two formations. The 
Jeffersonville limestone with Spirifer acuminatus as its most 
abundant fossil is the only division of the Devonian here. 
The Oriskany sandstone is absent from the Indiana sections. 
A sandstone known as the Pendleton sandstone resembles it in 
physical characters, and forms the base of the Devonian section 
at Pendleton, where it has a thickness of about 7 ft. The fauna 
of this sandstone, which is wholly unlike the Oriskany, has led 
to its correlation with the Schoharie grit of New York. 
TIME INTERVAL REPRESENTED 
The time interval represented by the hiatus at the base of the 
Onondaga and its western equivalents varies widely in different 
parts of the area which has been discussed. In the Wabash 
valley it marks the break between the Silurian and Devonian 
systems, while in parts of Ontario and New York a far briefer 
period within the limits of the Devonian system alone is represented. 
In the western area the time interval may be stated in terms of 
missing formations. These include the Salina, at the summit of 
the Silurian, and at the base of the Devonian the Helderberg 
limestone and the Oriskany sandstone. In New York and Ontario 
the relationship of the Onondaga and subjacent beds is of the 
character designated as a disconformity by Dr. Grabau, the beds 
showing no discordance of dip on the two sides of the unconformity. 
In northern Indiana, however, there is in some sections distinct 
though moderate discordance between the unconformable beds, 
or clino-unconformity. 
The place of the longest time interval represented by the strati- 
graphic break at the base of the Onondaga and its western equiva- 
lents as measured by missing formations coincides with the area 
