100 ANNUAL REPORT 7 
Fig. 43.—Columns for Supporting Roof of Filtration Chambers, Philadelphia, Pa. 
Otay Dam.—The Otay dam, figures 45 and 46, near San Diego, 
Cal., illustrate such a use of cement. This dam is 350 feet long, with a 
greatest height of 84 feet above the foundation. It is constructed in the 
