Ulrich 071 Correlation of the Lower Sihvrian. 307 
tinguished by recognizable, though slight, changes in both their 
lithology and fauna.' 
a The thickness of this subdivision in the vicinity of Cincin- 
nati is between 75 and 80 feet, but only 50 of these are exposed 
in the Kentucky bank of the Ohio river opposite the city, the 
lower 25 or 30 feet being below low water mark. In go- 
ing up the river, however, more and more is brought to the 
surface, till near Point Pleasant the whole thickness may be 
seen. The character of the lower 15 or 20 feet in the Ohio 
river exposures is not fully established, and I can speak of them 
only in the light furnished by well-borings at Covington and 
Cincinnati.' These appear to show that they are composed of 
dark shales, and twelve or more 3 to 8 inch courses of either 
subcrystalline or impure hard limestones, the latter apparently 
the more numerous. Both the shales and limestones contain an 
abundance of trilobite remains, of which those belonging to two 
or three species of Asaphtcs are by far the most numerous. 
The valves of several species of Beyrichia^ Pr'wutia and Cy- 
theropsis are also vei'y numerous, but other fossils seem to be rare. 
Several of the well-borings at Cincinnati seem to show that 
the contact between beds X and XI a is well marked, the pas- 
sage of the drill from the shaly layers of the latter into the 
tough heavy-bedded limestones of the former being abrupt, 
Still, I am inclined to believe that to the south and east of that 
city some localities will be found where the passage from the 
one into the other is not so abrupt. Such a locality probably 
exists along the Kentucky Central R. R. not far north of Paris, 
Ky. Carloads of rock brought from that vicinity and used for 
ballast by the Ky. Central R. R. Co. certainly resemble some 
of the layers of XI a. The rocks are full of fossils, of which 
among others chai'acteristic of beds XI a, Orthis borealls Billings 
and Rhynchonella increbescens Hall, have not been found above 
beds X in central Kentucky. 
1 It is to be observed here that xirt is nearly equivalent to the River 
Quarry beds, and y.\b to the Eden shales of Prof. Orton (Geol. Surv. of 
Ohio, vol. i) 
2 The writer hopes soon to make a careful examination of the Point 
Pleasant section so as to determine, if possible, the exact position of the 
strata there exposed. 
