GEOLOGY AND PALEONTOLOGY. ihayk 
and the yellow clay from No. 3, treated by the dry process, makes a buff or 
cream-colored pressed brick superior to the Milwaukee product. The mottled 
clay when used alone produces a red and white mottled brick much in demand 
for ornamental fronts, and the clay from the same beds is used by the Lincoln 
pottery for the manufacture of its products. 
Along the bluffs of the Big Sioux river, near Sioux City, Iowa, the clay be- 
tween the Dakota and the Benton is excavated from a bank some sixty feet in 
thickness. In general, the clay at this locality is bluish drab or gray, and re- 
minds one of the lower stratum at Yankee hill. Several companies are engaged 
in the manufacture of brick and tile at this place. At Sergeant’s bluff, Iowa, 
nine miles below Sioux City, there are two plants engaged in the manufacture of 
brick. The material is obtained from a bank a quarter of a mile long, and in 
general appearance resembles the Sioux City clay. On the hill north of the 
Platte river, opposite Louisville, is a bank from which the clay is shipped to 
Omaha, and there made into brick and tile. At Beatrice, the material from the 
Dakota beds have been extensively manufactured into brick, as also have the 
claysobtained near Endicott. An enumeration of the localities containing avail- 
able brick clay would simply be a catalogue of outcrops throughout the two 
states. There is scarcely a square mile of the Dakota that could not furnish 
sufficient clay to make brick to build a city. 
COAL, 
The coal of the Dakota group is inferior in quality and limited in amount. It 
is a lignite, or, as the popular phrase hasit, ‘‘brown coal.’’ This lignite is found 
throughout the group, from Oklahoma to South Dakota, ranging from the Per- 
mian or Comanche to the Benton. Knowing what we do of the conditions under 
which the deposits were made, we should be surprised not to find evidences of 
masses of decayed vegetation. In general, the conditions differed not materially 
from those that obtained in the Carboniferous age. The trunks and branches of 
trees, which in this case were dicotyledons instead of acrogens, blown down by 
the wind or swept away by the current, lodged in sheltered coves and were cov- 
ered with sediment. These drift accumulations have since been converted into 
the lignite which is found today. The conditions have not been favorable to the 
production of harder coals, except in isolated and very limited areas. 
Half a mile south of Bond’s mill, Washington county, Kansas, several thin 
seams of lignite are found within a few feet of the underlying Permian. At the 
High banks, near Decatur, Neb., similar seams appear at the water’s edge, prob- 
ably about the middle of the group. In describing a bed of lignite near the 
mouth of Iowa creek, west of Sioux City, Doctor Hayden says that it is in the 
Benton, or at least in the transition between the Dakota and Benton, and that it 
is local or restricted in its geographical extent, and is the result of the accumu- 
lation of drift in the Cretaceous sea. 
It is in the Smoky-Blue area in north-central Kansas, however, that the beds 
attain sufficient importance to be of commercial value. Even here they vary 
much in thickness. Some beds are two feet thick. Usually they are much 
thinner. Not infrequently the lignite is altogether wanting. It is found inter- 
spersed between beds of sandstone and shale, with often beds of carbonaceous 
shale near by. The horizon is usually from 60 to 100 feet below the Benton. 
The coal is most frequently obtained by stripping or removing the ledge near the 
surface. Occasionally shafts are sunk from the surface to the level of the lignite. 
These shafts are sometimes as much as seventy-five feet deep. Although the 
coal is of such poor quality, the price at the mouth of the shaft is usually as high 
as that of good coal in regions where the latter is plentiful. 
