558 A. F. FOERSTE 



the bridge northeast of town there is an exposure of Clinton 

 limestone, 20 feet thick. 



At Montgomery's Mill the limestone referred to the Laurel 

 bed is 28 feet thick : the Waldron bed, 4 feet ; the Louisville 

 bed, 25 feet thick, is unconformably overlaid by the Black shale 

 series; the original thickness of the Louisville bed at this local- 

 ity is therefore unknown. 



South of Centreville no exposures extending from the Ordo- 

 vician to the Waldron horizon are known until Riverside, 25 

 miles distant, is reached. The upper part of the Mannie clay, 

 5 feet 9 inches thick, is exposed northwest of Riverside, on the 

 western side of the Buffalo River, immediately north of the rail- 

 road bridge. It is overlaid by a massive bed of limestone, 5 

 feet 9 inches thick, strongly cross-bedded, very ferruginous in 

 places, referred to the Clinton horizon. Several hundred yards 

 north of the bridge, at the base of a large bluff, the top of this 

 cross-bedded limestone contains Silurian fossils. Here the 

 Clinton is overlaid by soft, rather thin-bedded limestone, 4 feet 

 thick, weathering back. A slight unconformity exists between 

 this soft limestone and the layers immediately above. The soft 

 limestone beneath this line of unconformity probably occupies 

 the Osgood horizon, although the base of the Laurel bed at this 

 locality is also soft, and weathers back, so that it cannot be dis- 

 tinguished lithologically from the Osgood bed. Immediately 

 north of the railroad bridge the Osgood bed appears to be 

 absent ; this is probably due to the unconformity already men- 

 tioned. 



Immediately above the cross-bedded Clinton, north of the 

 railroad bridge, the base of the Laurel bed contains numerous 

 specimens of Pisocritius gemmiformis , one specimen of Holocystites 

 4 inches long, and several specimens of large species of Ortho- 

 ceras. At the cliff, farther northward, the thickness of the 

 limestone referred to the Laurel bed is 36 feet 3 inches. The 

 upper half of this limestone is more massive, and some of the 

 courses are slightly reddish in color ; the lower part is softer and 

 weathers back. The Waldron bed is 3^ feet thick, and consists, 

 in ascending order, of clay, 14 inches thick ; soft white crumbling 



