J'ariatioiis of the Ordoi'iciaji of Indiana. — Foci'stc. 93 
South of Madison, HcbcrtcUa inscnlpta is unknown. Cer- 
tain facts, however, suggest that some opinions may be formed 
as to the variation in thickness of the southern extension of 
the intervals between the base of the HchcrteUa inscnlpta lay- 
er, the base of the Waynesville and the base of the Madison 
bed, notwithstanding the absence of Hchertclla inscnlpta. 
These facts are as follows : 
h. Thickness of Hchertclla inscnlpta layer. 
In Franklin county and at St. Leon in the northern part of 
Dearborn county the Hchertella inscnlpta layer has a thickness 
of seven feet. Northeast of Moores Hill on Hogan creek, also 
two miles east of Cross Plains, it is five feet thick. South of 
Cross Plains it diminishes rapidly in thickness. Its thickness 
is only 1.5 feet three miles southeast of Cross Plains in the 
northwestern corner of section three, and at most points in the 
northeastern part of Jefiferson county. Farther south, careful 
search often is necessary to secure specimens enough to make 
the identification of the Hchertella inscnlpta horizon certain. 
c. Interval bctzvecn Hchertclla inscnlpta layer and hase 
of Dinorthis subqnadrata zone. 
Dinorthis snbqnadrata entered the field later than H. in- 
scnlpta. The base of the D. snbqnadrata zone usually is sep- 
arated from the top of the H. inscnlpta layer by a short inter- 
val. At the north this interval apparently is greater than at 
the south. Thus at St. Leon, the lowest specimens of D. snb- 
qnadrata occur about eight feet above the H. inscnlpta layer. 
Farther south the interval is five feet ; for instance, in section 
3. three miles southeast of Cross Plains, on the Poplar 
Ridge road three and a half miles south of Cross Plains, in the 
southwestern corner of section 19 six miles southwest of Cross 
Plains, two miles northwest of Canaan on a branch of Indian- 
kentuck, and two miles southeast of Belleview on a road cross- 
ing Indiankentuck. Two miles east of Cross Plains the inter- 
val is 3.5 feet. Two miles northeast of IMadison on the road 
to Canaan the interval is only two feet ; this appears to be the 
interval also at Madison. 
d. The Vertical Range of Dinorthis snbqnadrata north 
of Madison. 
Half a mile southwest of Cedar Grove, on the road to 
South Gate, Dinorthis snbqnadrata has a vertical range of 140 
