STATE GEOLOGIST. 197 
with a smooth surface composed of one part cement and two parts of 
granite, or other suitable screenings, or sand applied in a, layer 1 to 
1%. inches thick. This must be put in place with the last course of 
concrete. 
(3) In arch tops, a thin coat of mortar or grout shall be applied 
over the top to thoroughly seal the pores. 
Proportioning. 
PARTS BY VOLUME 
STRUCTURE. 
Broken 
Cement. Sand. Gravel. Stone. 
The proportion of the materials in the concrete shall be as specific- 
ally called for by the contract, or as set forth herein, upon the lines 
left for that purpose; the volume of cement to be based upon the 
actual cubic contents of one barrel of specified weight. 
H. G. Ketiry, Chief Engineer, Minneapolis & St. Louis Railway, Minneapolis, 
Minn., Chairman; 
W. L. BRECKENRIDGE, Chief Engineer, Chicago, Burlington & Quincy Railroad, 
Chicago, I1l., Vice-Chairman; 
EK. C. Brown, Engineer Maintenance of Way, Union Railroad, Port Perry, Pa.; 
M. W. CooLtrey, Consulting Engineer, Boston, Mass.; 
JOHN DEAN, Consulting Engineer, St. Louis, Mo.; 
C. F. W. Fett, Chief Engineer, Gulf, Colorado & Santa Fe Railway, Galveston, 
Tex.; 
W. BE. Hoyt, Consulting Engineer, Rochester, N. Y.; 
©. Lewis, Civil Engineer, New York, N. Y.; 
G. F. Swain, Professor of Civil Engineering, Massachusetts Institute of Tech: 
nology, Boston, Mass., 
Committee. 
