March, 1908.] Devonian Section on Ten Mile Creek. 
27 3 
Columbus limestone. 
(j. Very fossiliferous crystalline gray limestone, 
the upper surface near the highway bridge 
showing fine glacial striae. 13' 
5. Compact brown limestone in massive beds and 
containing a few fossils in the upper part. . . 42' 
Silurian. 
Lucas limestone. 
4. Compact drab limestone showing a banded struc¬ 
ture. These layers are quite massive but 
weather into much thinner layers. Several 
fossiliferous horizons occur near the middle of 
the zone. 63' 
3. Compact drab limestone with some dark gray to 
brown sandy layers. This zone is brobably 
the basal portion of the Lucas limestone rather 
than a part of the underlying formation. . . . 36' 
Sylvania sandstone 
2. A fine grained friable white sandstone becoming 
coarser and of a conglomeratic nature in the 
lower part. The extreme base is made up of 
limestone pebbles imbedded in the sandstone 43' 
Tymochtee formation. 
1. Rather thin bedded compact drab limestone 
exposed at the bottom of the sandstone quarry 
at Silica but better along the creek to the east 
and south. 20' + 
The line of division between the Silurian and the Devonian 
is not sharply marked at this place. The change in the character 
of the depoists from one system to the other is, however, suffi¬ 
ciently great to allow the demarkation of this contact within a 
few inches or a foot at most. When it is recalled that this is the 
contact between formations of early or middle Cayugan and upper 
Ulsterian, it is surprising that the horizon is so ill defined, since 
it must have been an erosion or weathering surface for a long 
time. On the Maumee River near Grand Rapids, just across the 
southern border of Lucas County, the contact is shown and 
appears as a rather sharp line. Near Columbus, in the central 
Ohio region, decided evidence of the erosion period which inter¬ 
vened is found in the well developed basal conglomerate’of the 
overlying Columbus limestone. 
Along Ten Mile Creek the strata dip to the northwest at an 
angle which varies frome one to ten degrees. At no place along 
the creek does the elevation of the strata above drainage exceed 
eight feet;hence the major part of the section was determined by 
