Still , the rock layer here contains five to 30 percent phenocrysts , and has high levels of devitrification and lithic content .
Instead , erosion ate away at it , in the form of acid leaching , and broke down much of its pumice content .
The rock layer here contains five to 30 percent phenocrysts , and has high levels of devitrification and lithic content .
Instead , erosion ate away at it , in the form of acid leaching , and broke down much of its pumice content .