
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1917
1919
1920-1925
circa 1915
1915-1925
1923 - 2015
1920 - 2007
1926
circa 1920
1927
1927
1915
1920
1915
1924
1928
1918
1920-1929
1915-1925
1916
1915
1927
1915
1920-1925
1917
1928
1918
1925
1924
1955; 1830
1915-1917
1918
1918
1915-1918
1925-1928
1916-1917
1928
1922-1923
1922-1923
1922-1923
1922-1923
1921
1920
2000-100 BCE
before 1928
circa 1920
1923
1915-1925
1920-1928