Note 30 — Chapter X

Professor Huxley, in his Physiography, has estimated that "at the present rate of wear and tear, denudation can have lowered the surface of the Thames Basin by hardly more than an inch since the Norman Conquest; and nearly a million years must elapse before the whole basin of the Thames will be worn down to the sea-level"; and Dr. A. Geikie, after a series of elaborate calculations, has postulated "as probably a fair average, a valley of 1000 feet deep may be excavated in 1,200,000 years." Taking these estimates as a basis, and allowing for an average height of three hundred feet, we roughly arrive at a period of about four hundred thousand years as the possible length of time which it has taken to form this beautiful valley. Professor Huxley may well say that "the geologist has thoughts of time and space to which the ordinary mind is a stranger."