The Niobrara Chalk. — Calvin. 153 
at the time of writing the note under consideration the com- 
paratively large Foraminifera, which may be seen with a good 
pocket magnifier, seem to have been overlooked. A few 
months later, however, Williston renewed his observations on 
the chalk of Kansas, and his report of these later investiga- 
tions contains the statement that "the deposit seems wholly 
formed of coccoliths, rhabdoliths and Foraminifera, with, 
perhaps, radiolarians and sponges."* 
The foregoing references selected from the mass of litera- 
ture appearing between September, 1841, and March, 1894. 
while incomplete as a bibliography relating to the physical 
characteristics and foraminiferal origin of American chalk, 
may yet help to make clear the successive steps whereby geol- 
ogists have been led from complete skepticism regarding the 
presence of chalk on this side of the Atlantic to the convic- 
tion that considerable portions of the Niobrara beds along the 
Sioux and Missouri are, in all the particulars relating to 
composition and origin, identical with the chalk of Europe. 
('(IMPOSITION OF THeNiOBRARA ChAEK IN THE SlOUX IUVER 
REGION. 
The characteristics of the Niobrara chalk are such that ex- 
haustive investigations with the microscope may be carried 
out with very little difficulty. In thin sections from selected 
typical beds the unbroken shells of Foraminifera are very 
conspicuous. They lie in close proximity to each other, and 
their inflated chambers, filled with crystals of calcite, some- 
times occupy more than one-third the area of the entire field. 
It is certain that more than one-fourth and in some instances 
probably one-third of the volume of the chalk is composed of 
foraminiferal shells still practically entire. The matrix in 
which the shells are imbedded is made up of a variety of ob- 
jects, the most numerous, and the most conspicuous under 
proper amplification, being the circular or elliptical calcareous 
disks known as coccoliths. The small rod-like bodies to which 
the name rhabdoliths has been applied are not very common, 
although their presence is easily detected with a moderately 
high power objective. 
Mingled with the coccoliths and rhabdoliths are numerous 
fragments that are evidently the debris resulting from the 
*Proc. Kansas Acad. Sci., Vol. XII, p. 100. 1801. 
