68 G NEW YORK STATE MUSEUM 



beyond the range of weathering. Richardson gives the follow- 

 ing density for the Kosendale rock. 



Nearest surface 



Light rock 2.83 



Dark rock 2 . 849 



Medium 



Light rock 2.815 



Dark rock 2 . 841 



Light rock , 2.827 



Dark rock 2 . 845 



The Fort Scott (Kan.) rock which is nearer the surface has 

 a density according to Mr Eichardson of only 2.73, the Round 

 Top rock, Maryland, is 2.731, the hydraulic limestone of Illinois 

 is only 2.667 and does not produce as dense a cement. It is 

 also desirable that the various ingredients of the rock should be 

 as thoroughly mixed in as possible. If the sand is coarse or 

 the clay in lumps or the carbonate in pockets by itself, the rock 

 is not adapted for making cement. Generally mere inspection 

 will supply information on this point, and the size of the particles 

 can be determined by dissolving a weighed fragment in acid and 

 determining the size and quantity of the insoluble particles of 

 sand remaining. The residue of the Rosendale rock found at 

 various depths is noted by Richardson as follows. 



Per cent of residue on sieve 200 mesh, 100 mesh, and 50 mesh 



Nearest surface 



Light rock 2.9 



Dark rock 



• • • 



Medium 



Light rock. 

 Dark rock 



• • • • • • 



• • •' • • •' 



• • • • • • 



Deepest 



Light rock .6 . 6 .4 



Dark rock 1.2 .6 .3 



J 



