638 



CEMENTS, LIMES, AND PLASTERS. 



Part of the superiority, as shown by these tests, of the basalt dust 

 to. normal sand is probably due to purely physical causes. In part, 

 however, it is probably due to the fact that the finely crushed basalt 

 acted as a puzzolanic material. 



Range and average composition of natural puzzolanic materials. 

 From the separate tables of analyses given in preceding paragraphs 

 the following table of average analyses have been prepared: 



TABLE 241. 

 AVERAGE ANALYSES OF NATURAL PUZZOLANIC MATERIALS. 



Puzzolanic materials in the United States. Volcanic ash and other 

 materials which may be expected to show puzzolanic action occur ex- 

 tensively in the western United States, but few tests appear to have 

 been made of their hydraulic properties. 



Mr. J. S. Diller, in a recent description* of the mineral resources 

 of the Redding district of California, has noted that a "tuff, bordering 

 the northern end of the Sacramento Valley, is very like the trass of the 

 Rhine Valley. This is especially true of that on Stillwater, near the 

 Copper City road, or east of Millville, and at a number of points on the 

 western side of the Sacramento Valley. The limestone and the tuff 

 are at several places within a few miles of each other, and there is reason 

 to believe that a good quantity of hydraulic cement may be made from 

 them within convenient reach of the railroad. This matter is of impor- 

 tance in the construction of large dams for irrigation or water-power 

 in the Redding region. Similar volcanic products occur in Arizona, 

 .and have been used locally as puzzolanic materials. 



* Bulletin 225, U. S. Geological Survey, p. 177, 1904. 



