94 
CEMENT MATERIALS AND INDUSTRY. 
I bull, 24J 
THICKNESS. 
The thickness of the St. Joe bed throughout the greater part of th< 
area in which it occurs is from 25 to 40 feet. But as there is in man; 
places no definite line of demarcation between the marble and the over 
lying chert, the upper limit of the marble is somewhat arbitrary. Ii 
some places in the eastern part of the area the chert rests directly oi 
the Ordovician rocks, showing the entire absence of the St. Joe, whil< 
at other places, as at one place in the vicinity of Marble City, th< 
chert is 100 feet and at another it is 250 feet above the bottom of the 
marble. In such cases, however, the upper part of the bed is of gra^ 
limestone similar to that interbedded with the chert elsewhere, but n( 
sharp line can be drawn between the red marble at the base and tl 
gray limestone overlying it, for the two gradually merge into eacl 
other. 
COMPOSITION. 
The chemical analyses given in the accompanying table show the 
St. Joe limestone to be a comparatively pure carbonate of lime. 
Analyses of St. Joe limestone. 
Marble 
City. 
Residue insoluble in hydrochloric acid 
Titanic oxide (Ti0 2 ) 
Phosphoric acid (P 2 5 ) 
Alumina (A1 2 3 ) 
Ferric oxide ( Fe 2 3 ) 
Manganese oxide ( Mn0 2 ) 
Zinc oxide (ZnO) present, but not determined . 
Potash (K 2 0) and soda (Na 2 0) 
Magnesia (MgO) 
Lime (CaO) 
Loss on ignition ( C0 2 ) 
Total 
Carbonate of lime 
0.800 
Trace. 
.023 
.009 
. 051 
. 015 
Rhodes 
Mill. 
.054 
.190 
55. 390 
43. 740 
100. 272 
98.91 
0. 835 
Trace. 
.009 
.024 
.058 
.071 
.005 
. 160 
55. 340 
43. 630 
100. 177 
98.82 
Toma- 
hawk 
Creek. 
3.03 
.18 
.70 
.32 
.46 
53. 46 
42.30 
100.38 . 
95.46 | 
St. Joe 
crinoida 
1.1 
98. 
LIMESTONES OF THE BOONE CHERT. 
The Boone chert contains large quantities of limestone, some of the ; 
most valuable beds in the State occurring in it. In different parts of 
the region it varies widely both in quantity and quality. In some 
places it is made up almost entirely of limestone, while in others 
it consists almost entirely of chert. For convenience the subject is 
divided into three parts: (1) The limestone underlying the chert; (2) the 
