150 
CEMENT MATERIALS AND INDUSTRY. 
[BULL. 2^ 
magnesian or only slightly magnesian. In composition as in geolog 
position they are almost exactly equivalent to the famous cement ro( 
of the Lehigh Valle} T , from which 60 per cent of the Portland ceme 
of the United States now comes. 
Excellent exposures of the Trenton occur along the Mississip 
River and its tributaries in the counties named above. At Spec 
Ferry, in Dubuque County, the following section was observed: 
Fee l 
Specht Ferry section. 
1. Thin-bedded brown domolite with shaly partings (Galena) 
2. Thin-bedded, imperfectly dolomitized limestone, with fossil brachiopod 
shells only slightly changed; the limestone brown, earthy, noncrystalline, 
but evidently of the Galena type 
3. Thick, earthy, imperfectly dolomitized beds (Galena) 
4. Thin limestone beds with much shale in the partings; in part a true shale . 
5. Limestone, bluish, rather coarse grained, with a few fossils 
G. Limestone similar to above 
7. Limestone similar to above 
8. Shale, bluish or greenish, containing occasional thin beds or discontinuous 
flakes of limestone; the " Green shales" of the Minnesota geologists ... 
9. Thin-bedded, bluish, rather coarse-grained limestone, weathering brown- 
ish in color 
10. Limestone, in rather heavy layers, which range up to 15 inches in thick- 
ness; bluish on fresh fracture, but weathering to buff on exposure 
11. Brittle, fine-grained blue limestone, very fossiliferous, breaking up on 
weathered surfaces into flexuous layers about 2 inches in thickness 
12. Lower buff beds, exposed, about 
13. Unexposed to level of water in river 
COMPOSITION. 
The "Green shale' 1 No. 8 of the above section and the limestoi 
above and below were sampled and analyzed by Mr. Lundteigen w:> 
the results given below: 
Analyses of Trenton limestone from Specht Ferry section, Iowa. 
Silica (SiO a ) 
Alumina and iron oxide (Al 2 3 and 
Fe 2 3 ) - 
Lime (CaO) 
Magnesia (MgO) 
Alkalies by difference 
Sulphur (S) 
Loss by ignition (H 2 0, C0 2 ) 
7.28 
1.97 
46. 93 
2.58 
.39 
40.10 
99. 25 
2.25 
1.32 
49. 66 
3.24 
.42.80 
99.27 
46. 34 
19.90 
10.27 
2.13 
.01 
13.90 
92. 55 
2.58 
41.32 
5.80 
.00 
40.00 
5.00 
2.07 
50. 22 
.85 
.76 
.85 
40. 25 
98. 68 100. 00 
<; 
54 
25 
10( 
1. Beds 5 and 6. 
2. Bed No. 8. 
3. Bed No. 9. 
4. Bed No. 10. 
5. General sample of limestone. 
6. General sample of clay. 
