Figure F22. Diagram of SiO₂ vs. total alkalies (Na₂O + K₂O) abundance showing the compositions of Site 1136 samples. The boundary between tholeiitic and alkalic basalts is from Macdonald and Katsura (1964). Open symbols = samples from Unit 1; solid symbols = samples from Unit 2; circles = fresh samples; open square = Sample 183-1136A-15R-2 (Piece 2, 69-71 cm) (altered basalt); solid square = Sample 183-1136A-18R-4 (Piece 2, 89-92 cm) (vesicle-rich segregation).