Note 93 — VI
Reading edition
See an interesting and suggestive paper by Professor Le Conte on 'Critical Periods in the History of the Earth,' Bull. Dept. Geology, University of California, vol. i. (1895), p. 313; also one by Professor Chamberlin on 'The Ulterior Basis of Time-divisions and the Classification of Geological History,' Journal of Geology, vol. vi. (1898), p. 449.