Source: https://www.cambridge.org/core/services/aop-cambridge-core/content/view/45F5A210AB6833FCF6ECE58FA5909B55/S0016756800090166a.pdf/a-textbook-of-geology-by-philip-lake-ma-fgs-and-e-h-rastall-ma-fgs-pp-xiv-and-508-third-edition-1920.pdf