U. S. GEOLOGICAL SURVEY 
BULLETIN NO. 324 PL. XXV 
A. SUBSIDENCE OF STREET IN FRONT OF /ETNA BUILDING, SAN FRANCISCO. 
Photograph by John Stephen Sewell. 
-•--.. 
]!. FIRE ENDURANCE OF CONCRETE, ANNEX OF ACADEMY OF SCIENCES BUILDING, 
SAN FRANCISCO. 
Reenforced-concrete floors and concrete-filled cast-iron columns with plaster covering. Photograph by 
Richard L. Humphrey. 
