Congrès géologique international, Congrès géologique international… (1891)
“ But who can determine beyond a doubt whether a recent lava is Quaternary or Pre-Quaternary, or why shall we distinguish practically identical rocks by separate colors, because one happened to be erupted before and the other after an imaginary period of time ? It, moreover, seems of doubtful advisability to attribute the importance of being one of the seven great divisions of eruptive rocks to a material like serpentine, which is always the product of alteration of some other rock or mineral, and probably quite as often of sedimentary as of eruptive rocks or minerals. ”
