The Niobrara Chalk, — Calvin. 14:5 
series that was long ago made classic by the labors of Meek 
and Harden. The work of Hill and others in Texas enables 
us now to refer the beds in question to the Upper Cretaceous, 
as distinguished from the Comanche <>r Lower Cretaceous 
series of the Southwest. In the region we are considering the 
Cretaceous begins with the Dakota sandstone, a formation in- 
dicative of shallow seas and moderately high contiguous 
chores. During the deposition of the Dakota beds the water 
over what we now call Sioux City was shallow and vexed 
sometimes with conflicting currents, as is shown by the eross- 
bedded sands with oblique planes inclined in many different 
directions. That the land was high enough to enable the 
drainage waters to carry coarse mechanical sediments, that it 
was covered with semi-tropical forests of deciduous trees, and 
that its surface was watered with a most generous rainfall, 
are clearly recorded in the material composing the deposits, 
in the taxonomic relations of the leaves and Other organs that 
make up the profusion of fossil plants which some of the beds 
contain, and in the brackish-water types composing the rather 
meager molluscan fauna of the earlier layers. Moreover the 
region was part of a great area of subsidence. H we limit 
attention to some given point, for example the bluffs above 
the mouth of the Sioux river, we shall find certain facts 
(dearly recorded. During the entire time represented by the 
CFpper Cretaceous there may have been many alternations of 
elevation and subsidence, but at first the waters were gradu- 
ally deepened and the shore line became more and more re- 
mote. As these processes went forward the coarser sediments, 
together with the leaves and twigs of the magnificent foresl 
flora clothing the land, all came to rest in the beds laid down 
near the constantly receding shore, and only the finer (days 
were carried seaward as far as the point we have selected for 
consideration. With progressive subsidence the land stood 
lower, the drainage streams became more sluggish, erosion was 
less energetic, and it is probable that at this stage even in the 
marginal sediments the materials were fine day with little 
admixture Of siliceous sand. At all events, at a short dis 
tance from the shore we have the transition from Dakota 
sands, with some alternating beds of shales, to the purer Fori 
Benton (days, which represent the second phase of sediraenta- 
