STRATIGRAPHICAL GEOLOGY 
251 
formations in which these salt beds occur, may have been wide¬ 
spread, reaching possibly from western Oklahoma southwestward 
to the Pecos River. The largest part of this area lies in Texas. 
Udden. 
Mid Ordovicic Volcanic Ash in Tennessee. A deposit of vol¬ 
canic ash, known as bentonite, was recently disclosed in the 
grading of the Dixie Highway east of Shelbyville. This bed, 
according to E. S. Larsen, is a decomposed rhyolitic ash, some¬ 
what akin to leverrierite which has been greatly altered immediate¬ 
ly after eruption. 
It occurs in the top of the Carters formation (Lowville), of the 
Mid Ordovicic section. This stratum is 21 inches thick; and is 
divided into three distinct layers. At the top of the bentonite 
is a half-inch streak of white, hydrated calcium carbonate; then 
10 inches of green bentonite, with streaks of white hydrated 
calcium carbonate extending through it in nearly vertical lines; 
then five inches of yellowish, sandy bentonite, containing rounded 
grains of quartz, black mica and feldspar; and a basal layer of 
five inches! of green bentonite, resting upon the smooth surface 
of dark blue, crystalline limestone. The junctures between the 
three layers of bentonite bed are very regular; but the contact 
between the top of the bentonite and the overlying limestone is 
irregular, and, in places, this dove-colored, thinly bedded limestone 
cuts down to within one or two inches of the top of the second 
layer of the bentonite bed. 
Other samples of bentonite have also been obtained from well- 
cuttings in Pickett and Overton Counties, and from McMinnville, 
in Warren County. An outcrop of the bed at Pruetts cut, near 
Watertown, in Wilson County, was recently described by the 
writer, that was thought to be bentonite, but no good samples 
could be obtained for tests. 
Ulrich mentions a bed of clay occurring at the horizon of the 
Carters formation, at High Bridge, on the Kentucky River, in 
Kentucky, which recent investigations show to be this same ben¬ 
tonite bed. At Birmingham, Alabama, a layer of bentonite, which 
is probably the same as the Tennessee layer, was found within 
30 feet of the top of the Ordovicic succession, in the bottom of 
the shafts of the Tennessee Coal, Iron and Railroad Company. 
