March, 1908.] Devonian Section on Ten Mile Creek. 273 



Cohimbus limestone. 



6. Veiy 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' 



SiLURIAK. 



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 grav 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 quarrv 

 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 Cavugan and upper 

 Ulsterian, it is surprising that the horizon is so ill defined, since 

 it must have been an erosion or w^eathering 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 



