The Sfraft<tr(t/>f)i/ of X. W. Lou island. — VaiKjlKdi. 215 
his second rej)ort the name "Arcadia cla^'s" was given, and 
tliey were considered of Jackson age. 
The author was first led to doubt the existence of an un- 
conformity for paleontologic reasons. The Lower Claiborne 
attains a fine development in Louisiana. In Winn and Natch- 
itoches parishes, the Lower Claiborne beds, as already noted, 
become very calcareous, and Osfrea sello'formis is often found 
in the greatest abundance. These features are characteristic 
of Hilgard's CalcareoKs Claiborne in Mississippi, which has 
been correlated with the Osfrea selUvformis beds of Alabama 
by Smith. The Ostrea selUcformis beds in Alabama are sepa- 
rated from the Jackson by scarcely 30 feet of strata. Whether 
the calcareous beds of Winn and Natchitoches parishes are 
the exact equivalent of the Ostrea seila'formis beds of Ala- 
bama or not, the fact remains that they are not far from the 
base of the Jackson, and it seems improbable that a long pe- 
riod of dry land surface could have intervened. Furthermore, 
(x. D. Harris* in Arkansas discovered beds "Uppermost Clai- 
bornian or perhaps transitional between that and the Jack- 
son," a fact to my mind making it still more improbable that 
there could have been in Louisiana an erosion period between 
the two stages. 
In order to study this supposed unconformity further, in 
November, 1894, I went to Arcadia to examine again some sec- 
tions in that vicinity. Fig. 3, plate IX, represents a section 
made in the first railroad cut west of tliat town. The gray 
or Arcadia clays were found resting conformably on the 
black clays. The dip of both the gray and black clays was 
the same both in direction and amount, and the stratifica- 
tion was absolutely continuous from one clay to the other. 
From the distribution of the color one would at first be in- 
clined to think that there was an unconformity, but in a layer 
not thicker than one's finger I have seen the stratum in the 
length of about a foot, light gray or blue, then chocolate, and 
at last black (or almost black) where it passes into the lig- 
nitic nucleus of the cut. Fig. 4, a section made on the La. & 
N. W. railway, six and a half miles south of (Jibbsland, rep- 
resents the same phenomena. Instead of an unconformity, I 
would suggest as an explanation, that the waters working 
*'riTliai-\ (m'oIou'v (if Sdiil lii'i'ii Arkansas, n. iC!, 1S!)4. 
