640 THE JOURNAL OF GEOLOGY. 



time and the age of the earth. Soon after geology emerged 

 from its pre-systematic stage, in the latter part of the eighteenth 

 century, and assumed an independent position among the induc- 

 tive sciences speculations on the age of the earth began. Dr. James 

 Hutton, the founder of modern physical geology, and the prede- 

 cessor of Lyell, in advocating the uniformitarian theory, was the 

 first to argue that the rate of destruction of one land area was 

 the means of measuring the duration of others, and that the con- 

 tinents were formed of the ruins of pre-existing continents, but 

 that in our measurement of time such periods were of indefinite 

 duration. 1 It was not, however, until 1830, when Sir Charles 

 Lyell published the results of his profound and philosophic 

 studies of geologic phenomena, that the broad outlines of the 

 law of uniformity, as opposed to the doctrine of geologic catas- 

 trophes, was fairly established. This work rendered possible a 

 computation of the age of the earth on the principle that geo- 

 logic processes were the same in the past as at present. He 

 based his estimate of time on a rate of modification of species of 

 mollusca since the beginning of the " Cambrian period," and 

 divided the geologic series into twelve periods, assigning 20,000,- 

 000 years to each for a complete change in their species, — or 

 240,000,000 years in all. This estimate excluded the " antece- 

 dent Laurentian formation." 2 



The hour at our disposal does not permit of mentioning at 

 length the views of other geologists. Dr. Charles Darwin 

 thought that 200,000,000 of years could hardly be considered 

 sufficient for the evolution of organic forms, 3 and Rev. Samuel 

 Haughton assigned 1,280,000,000 of years to pre-Azoic time, 

 and remarked that the globe was habitable, in part at least, for a 

 longer period. 4 At a later date he estimated a minor limit to 



1 Theory of the Earth ; or an Investigation of the Laws observable in the Composi- 

 tion, Dissolution, and Restoration of Land upon the Globe. Trans. Royal Soc. Edin- 

 burgh, Vol. I., 1788, pt. 1, p. 304. 



2 Principles of Geology, 10th Ed., Vol. I., 1867, p. 301. 



3 Origin of Species, American Ed., from 6th Eng. Ed., 1882, p. 286. 

 * Manual of Geology, 3rd Ed., 1871, p. 101. 



