STATE GEOLOGIST. 55 
No. 9 shows the analysis of the Utica cement, mined at Utica, Ils., 
the rock being a clayey limestone of Lower Silurian age. 
No. 10 is a natural cement found at Round Top, Md. 
No. 11 is a Roman cement manufactured near patito, IN Woy Oil tae 
Rosendale type. 
No. 12 also is a cement of the Rosendale type, but manufactured at 
Milwaukee, Wis. : 
No. 13 represents the famous Lehigh Valley rok mined near Allen- 
town, Penn., in the villages of Copley, Siegfried and other places. The 
Roman cement made from this rock is of high quality and is also being 
used in the manufacture of Portland cement, limestone lower in clay being 
added to produce the correct composition. 
No. 14 is a cement rock obtained at Cumberland, Md. 
On examining the chemical composition of these hydraulic cements 
ibicerounds that the averace molecular ratio on R@:Si@s is) 1.60:1 and 
that the average oxygen ratio, RO:A1,O, :SiO, is 1.60:0.69:2. The vari- 
ations in composition, it will be noted, are very great indeed, and it seems 
as if the hydraulic activity were not a function of definite compounds, but is 
dependent on a pozzuolanic reaction which merely requires enough base 
to “unlock” the silica. The difference in the rate of setting of these 
cements is evidently governed by their content of alumina as well as of 
calcium oxide. Beside the chemical composition the uniformity of com- 
position of a rock deposit, its fineness of grain and intimacy of 
mixture of the carbonates and the clay must be carefully considered. 
Coarse, crystalline limestone with irregular patches of clay would not be 
suitable at all, the same being true of fine grained carbonates and coarse 
clayey matter. On dissolving a sample of cement rock in hydrochloric 
acid, filtering off the residue, treating it repeatedly with hot sodium car- 
bonate solution and finally washing out the reagents used, the residue of 
clayey matter can. be examined. The photograph on page 56 shows 
the residue thus obtained from) Rosendale cement, as seen under the 
lower power of a microscope. It was found to consist of amorphous 
clay substance, shown by the dull non-crystalline patches, more or less 
crystalline orthoclase fragments clouded around the edges by kaoliniza- 
tion, some flakes of mica and sharp edged crystalline fragments of quartz. 
RAW MATERIALS OF THE PORTLAND CEMENT INDUSTRY. 
The constituents introducing calcium oxide may be limestone, marl, 
slag, or industrial waste products. The clay components may be intro- 
duced as clay or mixtures of clay and sand, or as cement stone, a calcareous 
material high in clay base. In the great majority of Portland cement 
plants the mixture consists of two distinct components, the one introducing 
the clay, the other the necessary lime. The cement stones of the Lehigh 
Valley, containing more than the required clay, need the addition of a 
