GEOLOGY AND PALEONTOLOGY. 189 
EXPLANATION OF PLATE XIV. 
Aviculopinna nebrascensis. 
1. Concave cast of valve, showing markings. 
1b. Cast of type. 
le: Portion of another cast, showing direction of markings. 
1d. Figure showing outline of posterior of shell. All natural size. 
Aviculopinna knighti. 
2. Outline of young specimen. One-half natural size. 
THE AMERICUS LIMESTONE. 
BY ALVA J. SMITH, EMPORIA. 
Read before the Academy December 28, 1900. 
The limestone under consideration in this paper is called the Americus lime- 
stone on account of its being extensively quarried near that village. It was 
thus denominated by Kirk in his Neosho river section, and is referred to by him 
on page 80, volume I, of the University Geological Survey, but it seems to have 
escaped identification in other localities. 
The color of the Americus stone is a neutral drab, weathering to a light buff 
on account of the oxidation of the iron it contains. Its texture is even, com- 
pact, and semicrystalline; hardness, three. Its thickness varies in different 
localities, from sixteen to twenty-two inches, and it may be obtained in blocks 
of any required size. All points considered, it is by far the best building stone 
in Lyon county. 
An analysis of the stone yields the following’elements, approximately in the 
proportions given, viz.: 
SICA lOs) teria erent cu eie cle oonoretoers ers oes as 6 
Calciimucarbonaten(©a@ Os) reancemareeosece dee ee 75 
Aluminates and ferrous carbonate (FeCOs3)......... 12 
Meaonesiumicarbonaten(ic@ Os) see ssace sees oe 6 
101 
Fossil fauna are quite abundant, the upper portion containing great numbers 
of Fusulina cylindrica; while crinoid stems, Productus costatus, Productus 
semireticulatus, and Spirifer camerata and a species of Fetzia are occa- 
sionally found in the lower portion, the Retzia being very abundant in the 
shale above, while the yellow shale beneath is apparently barren of fossils. 
The adjacent strata, both above and below, are a series of thin-bedded lime- 
stones and shales, the shale assuming an arenaceous character about thirty feet 
below, while thirty-five feet above is the most productive /wsulina horizon that 
has come to my notice. They are there bedded together in a friable limestone 
about four feet thick, which disintegrates on exposure, freeing the little fossils 
by the million, so that they fill the soil in many places for hundred of yards be- 
low the outcropping formation. 
There is a locality on Wolf creek, in the southwest corner of Lyon county, 
section 19, township 21, range 10, where they may be gathered with a shovel. 
This horizon is a prominent feature in the series and may frequently be used to 
locate the position of the Americus stone when it is covered. 
The outcropping margin of the Americus stone may usually be recognized at 
a distance by the large, rectangular blocks, which are always in evidence where 
the ground surface isat all precipitous. Blocks measuring ten to twenty feet are 
