
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1920-1925
1917
1919
1923 - 2015
1920 - 2007
1926
1931
circa 1920
1927
1927
1920
1924
circa 1930
1928
1918
1920-1929
1932
1931
1931
1927
1930
circa 1930
1920-1925
1917
1928
1918
1932
1925
1924
1955; 1830
1918
1918
1925-1928
1928
1924
1927
1926
1922-1923
1922-1923
1921
1922-1923
1922-1923
1921-1926
1925
1920-1929
1920-1930
1920-1930
1923
1924-1927