
Obsidian possibly used in trephination experiments
1918-1920
1918-1920
1935
1935
1920-1925
1917
1934
1919
1920-1940
1936
1923 - 2015
1920 - 2007
1926
1931
circa 1920
1927
1940
1927
1938
1920
1924
1940
1938
1938
1938
1935
1938
circa 1930
1940
1928
1918
1940
1936
1920-1929
1934
1935
1922
1938
1938
1932
1932-1936
1934-1935
1934
1916
1937
1931
1931
1938
1936
1927
1925