In regard to subaerial denudation, Mr. Croll shows, by calculating the known amount of sediment annually brought down by certain rivers, relatively to their areas of drainage, that 1,000 feet of solid rock, as it became gradually disintegrated, would thus be removed from the mean level of the whole area in the course of six million years.
Erosio atmosferikoari buruz, Crollek, zenbait hibaik beren arroarekiko erlazioz urtean ekarririko sedimentu kantitatea kalkulatuz, frogatzen du herrialde guztiaren batez besteko altuerari, sei milioi urteren buruan harri sendarrezko 1.000 oin kenduko litzaiokeela era honetan, harriak poliki-poliki suntsitu ahala.