202 
CEMENT MATERIALS AND INDUSTRY. 
[BULL. 2' 
Third. A dark, grayish-black, fine-grained, hard, yet brittle, shale, which is app; 
ciably plastic when ground and mixed with water. Shale of this type is found 
several of the mines near Saginaw and Bay City, and is quarried at Flushing for t 
manufacture of paving brick. Similar shales are associated with coal seams ne 
Jackson and may be expected to occur throughout the area indicated as bei 
occupied by the Saginaw formation. 
The chemical composition of the shales just referred to is indicated by the folio 
ing analyses: 
Analyses of shales of the Saginaw formation. 
Constituent. 
Silica (Si0 2 ) 
Alumina ( A1 2 3 ) 
Ferric oxide (Fe 2 3 ) 
Calcium (CaO) 
Calcium carbonate (CaC0 3 ) . . . 
Magnesium ( MgO ) 
Magnesium carbonate (MgC0 3 ) 
Sodium oxide (Na 2 0) 
Potassium oxide (K 2 0) 
Water and organic matter 
Total. 
FeO. 
54. 50 
30.75 
3.50 
1.05 
1 69 
.80 
2.20 
5.51 
100.00 
52.45 
23.27 
7.93 
1.82 
1.06 
4.37 
9.10 
100. 00 
1.57 
57.10 
20.02 
8.18 
.71 
1.47 
2.76 
9.76 
100.00 
1.47 
61.13 
26.90 
1.12 
.96 
(?) 
(?) 
6.47 
96.58 
54.93 
31.43 
.22 
1.58 
(?) 
(?) 
7.44 
95.60 
41. 
27J 
(?) 
(?) 
23.: 
92. < 
1. Fine-grained, black shale from Flushing. Analyst, H. Ries. Geological Survey of Michiga 
vol. 3, pt. 1,-1900, p. 30. 
2 and 3. Shales associated with coal at Bay City. Analyst, A. N. Clark. Ibid., pp. 35-36. 
4, 5, and 6. Coal mines at Bay City. Analyses furnished by the Hecla Portland Cement and Co i\ 
Company. Analysts, Lathbury and Spackman. 
As shown by these analyses, the shales of the Saginaw formation as a rule ai 
lower in silica than is deemed desirable for use in making Portland cement, bv 
certain beds have been recommended by experts in that industry. Evidently an 
layer of shale in the Saginaw formation which can be economically mined, an| 
which is free from sand and other objectionable substances visible to the eye, shoul 
be carefully tested and experimented with in connection with the industry und€ 
review. 
CLA YS. 
Surface clays deposited during the Pleistocene period of geological history — ths I 
is, at a late date, and after the land had about its present relief — are abundant 
throughout Michigan. These clays were in part left on the surface of the countr 
directly by the glaciers during the last ice invasion of the Glacial epoch, or in som 
instances by streams flowing from the glaciers; in part were laid down in small lake 
and in the waters of the Great Lakes when more widely expanded in certain direc 
tions than at present, and in part were spread out in the flood plains of streams 
These three varieties may be termed, to adopt the classification used by Ries/' drif 
clays, lake clays, and river silts. 
The drift clays are invariably calcareous and usually contain sand, stones, an< 
bowlders, and show much variation in composition. They are the most abundant o 
«Geol. Survey Michigan, vol. 8, pt. 1, 1900, pp. 48-62. 
