Devonhiii Series in Southirestent JI issoin-i. — llersheij. 295 
veloped at the town of Eureka Springs, Ark., where it is the 
chief cause of the emergence of most of the springs at a given 
horizon; and from this town it has received the name of Eu- 
reka shale. Its Devonian age is inferred chiefly from its 
stratigraphic relations, it being (conformable to the base of 
the Kinderhook group, also well developed in this region. 
In portions of Stone and Barry counties, where it has been 
studied by the writer, it was found to be underlain by strata 
of limestone, and even a thin bed of sandstone intervened be- 
fore the top of the Ozark series was reached. From an exam- 
ination of numerous outcrops the following section has been 
prepared : 
Thickness. 
1. Eureka shale 7 feet 
2. Gray shaly limestone 13 " 
3. Speckled crinoidal limestone 3 " 
4. Basal sandstone 1 " 
Where studied by the writer, the Eureka shale consists of a 
bed of flnely laminated, soft, argillaceous shale, generally 
somewhat calcareous, especially in certain layers. Its color, 
on exposure, varies from a light green to a dark blue gray; 
and it is probably, before being exposed to the atmosphere, of 
a very dark and perhaps even black color. Hence, when pen- 
etrated by wells or other excavations, it would be reported as 
a black shale, while if seen only on exposed surfaces it would 
be considered a green shale. It is nearly or quite destitute of 
fossils, hence its paleontologic position cannot be determined 
with certainty. A characteristic of it is the occurrence of 
satin spar as a secondary mineral in thin layers and in verti- 
cal veins. 
The Eureka shale passes downward by interstratitication 
and intergrading of materials into the next division of the 
Devonian strata in this region, a bed of light brown and gray 
shaly limestone. The limestone is evenly but rather thinly 
bedded, and varies locally from a very argillaceous to an al- 
most purel}^ calcareous composition. It also varies greatly 
from layer to layer, sometimes being a nearly pure limestone, 
with macroscopically an "amorphous" or non-cry>^talline tex- 
ture, alternating with other strata of a distinctlj" shaly struc- 
ture. The compact "amorphous" limestone contains no fos- 
sils, or only a few scattered here and there: but the more 
