150 KANSAS ACADEMY OF SCIENCE. 
usually weather into gentle slopes, which are almost uniformly grass covered. It 
is only along the steep banks of streams or in artificial exposures such as rail- 
road cuts that typical exposures of the clay may be seen. It is the opinion of 
the writer, after having studied the group in thousands of exposures, in four 
states, that at least two-thirds of the rock consist of clays and shales. 
The character of this material is by no means constant. From a very are- 
naceous shale, with the prevailing yellowish-brown color, it grades through varie- 
ties less and less sandy; until finally in not a few places may be found dark-blue 
and almost black papyraceous shales and clays, resembling in lithological ap- 
pearance those of the marine Kiowa. Between these two extremes of color are 
endless varieties and shades, with red, pink, yellow, cream and white predomi- 
nating. Oftentimes all these colors may be seen in the same clay bank. Notin- 
frequently thin, lenticular ledges of sandstone or concretions of various shapes 
and sizes are found embedded in the shale. These concretions, being normally 
of a dark reddish-brown color, and breaking with a conchoidal fracture, often 
render the slopes conspicuously brown. This clay is probably designed to be- 
come the most valuable economic product of the Dakota. The large and varied 
amount of iron contained in it, which causes the differentiation of colors, con- 
stitutes it a very superior brick and tile clay. The pottery products are also ex- 
ceptionally fine. 
In a number of localities brick-works which obtain their material from Dakota 
clay banks are in operation; and when experience shall have demonstrated the 
superiority of the products these plants can but increase. The sandstone of the 
Dakota, as has been shown, can never have more than a local value. Coal is 
limited in quantity and poor in quality, sand is found elsewhere, and gravel is 
not plentiful in this formation. The clay, on the other hand, being inexhaustible 
and of excellent quality, will be wrought more and more and the products shipped 
to distant localities. 
The Yankee Hill Brick and Paving Company operates a plant three miles 
southwest of Lincoln, Neb., which may serve as a typical representative of the 
brick-works of the Dakota area. The clay is in this case obtained from a horizon 
a little above the middle of the group, probably about 100 feet below the Benton. 
Something like three acres are included in the bank, although tbe material in 
sight covers over 100 acres. Above the Dakota at this locality are some twenty 
feet of glacial drift and loess. From this material a certain kind of brick is manu- 
factured. The following section, taken in a typical part of the bank, will indi- 
cate the sequence of the beds: 
Mo: Giolla, Sete fo ek iwc B bh eee ae ee 5 feet 
INO. 5. EGGS ak Sree heen Naas allo. J clntin See abe eae ees 10;e3 
No. 4. -Drift‘sbouldersiand pebbles .2-. 2:2 Bh. exci ne nel ya ME 
No. 3. Yellowish, sandy clay, known as ‘‘ bastard fire-clay’’.. 3 ‘* 
No. 2. Red, pink and white mottled clay .................. Gs 
No. 1. Sleek, blue-grayielay shale... .: 2 6.405.0.deiviee ston OME 
A hundred yards from the place where this section was taken the red and 
white mottled clay, No. 2, occupies nearly the entire thickness of the exposures; 
again, the yellowish fire-clay is more pronounced; while a quarter of a mile away, 
just over a small hill to the west and approximately on the same level, the clays 
have given place almost entirely to coarse, soft sandstone. 
Experience has proven that a judicious mixing of the clays from the various 
horizons produces several different qualities of brick. The ordinary building 
brick is obtained by using two parts of the red mottled clay from No. 2 and one 
part of the loess, or No. 5; Nos. 1 and 2 in equal quantities make paving brick; 
