1886. ] l Geology and Paleontology. 637 
much interest, more especially in reference to their geological 
and geographical distribution. . 
NOTES ON THE VARIATION OF CERTAIN TERTIARY Fossits IN 
OVERLYING Beps.—In the Southwestern Old-tertiary there are 
some high vertical exposures, which show different fossiliferous 
beds vertically above each other. One of them is the file 
1885, p. 71. The “ Higher Vicksburgian,” consisting mainly of 
reddish sands, contains those fossils usually known as Vicks- 
burgian fossils ; the bed, “ Lower Vicksburgian,” a dark grayish 
marl, contains a very similar but not entirely identical and less 
humerous fauna; both are separated by about thirty feet of lime- 
stone. Some of the lower species are not known from the higher 
bed, which, however, is at least partly owing to different methods 
of collecting in both beds. The main number of species of the 
lower bed occurs also in the higher one. In most of them, for 
Instance, Buccinum mississippiense Conr., Sigaretus mississippiensis 
Conr., Pleurotoma congesta Conr., Murex mississippiensis Conr., 
Terebra divisura Conr., Trochita trochiformis Lea, Turritella cæla- 
aD 
ferences ; Cytherea sobrina Conr. from the lower bed is in gen- 
eral longer than from the higher bed. Ten specimens of the 
higher bed, taken without special selection, showed, if the height 
to 1.33, 
an average of 1.30. More striking is the relation of the two : 
forms of Ficus mississippiensis Conr., which species in the lower 
o 
age and size in both varieties, the higher variety shows one more 
System of revolving lines. This difference between the two varie- 
hes is not very striking, but is large and constant enough to dis- 
tinguish the forms of the two beds without reference to the litho- 
logical contents of the shells. The following diagram represents 
the plan of the origin of the revolving lines as they can be traced 
along the volutions of each form: 
4, 
ra NAE E E / E 
. ee 
ee i i ey i ty 
Pee 
= 
pr ines of the form of the “Lowėr Vicksburgian ;” II, lines of the form * p 
A 1 urgian,” ; $ Jag 
“Higher Vicksb 
r F. 
