UNCONFORMITY AT BASE OF ONONDAGA LIMESTONE 317 
there is no discordance in the dip of the strata on the two sides of 
it, but in the Wabash valley discordance between the Silurian and 
Devonian limestones is distinctly marked at many outcrops. In 
this area the term clino-unconformity recently proposed by Pro- 
fessor Crosby‘ is applicable. The Silurian rocks at many points are 
highly tilted, while the Devonian beds lie nearly horizontal, thus 
Fic. 8.—Showing discordance in dip of the Devonian and Silurian limestones at 
Pipe Creek Falls in northern Indiana. 
affording unequivocal evidence of unconformity. Away from the 
immediate vicinity of the small local domes in the Niagara strata, 
however, the discordance between the Devonian and _ Silurian 
limestones, though slight, can easily be detected with careful obser- 
vation. Sometimes, however, the discordance is not noticeable. 
Just below Georgetown both the Silurian and the Devonian 
are exposed on each side of the Wabash River. From 5 to 8 ft. of 
gray crystalline Jeffersonville limestone rests on irregularly eroded 
Silurian limestone. The line of contact between the two is an 
™ Jour. Geol., XX (1912) 2096. 
