154 C. Lloyd Morgan — Geological Time. 



the pre-existing materials : so that if we assume a freer circulation of 

 underground heat below this crust than through it, as I think volcanic 

 action indicates, and a successive building up of crust upon crust as 

 it is destroyed from below, together with an intrusion of melted 

 materials which from time to time, as we know, has taken, and is 

 taking place, the conditions of varying increments of heat actually 

 met with in equal spaces downwards will be pretty well fulfilled. 

 That this circulation of heat takes place at great depths is rendered 

 probable by the alteration of the positions of volcanos from time to 

 time in the Earth's history, by the tremendous evidences of volcanic 

 effects in Tertiary times, and by existing volcanos.' 



Facts are safer than theories, and as at 100 miles deep, even 

 according to Sir W. Thomson's theory, the rocks now must be at 

 7000° Fahr., if this circulation of internal heat takes place as 1 suggest, 

 there is sufficient store of heat in the Earth now to carry us on com- 

 fortably for another 1000 million of yeai's, without those reconstructive 

 agencies on which our existence depends becoming impotent. 



II. — Geological Time. 

 By C. Lloyd Morgan, F.G.S., A.E.S.M. 

 (Part I.) 



ONE of the most important questions which modern geologists 

 have to answer is that M^hich refers to the duration of Geolo- 

 gical time. How long is it since the Glacial epoch? What was 

 the date of man's appearance on the earth ? How many ages have 

 rolled by since the earth first became the habitation of organized 

 beings ? Such are the questions, daily repeated, to which we must 

 make some answer, or, if need be, honestly confess our ignorance. 



It is interesting to notice the change which has taken place, 

 within the last century or so, in the opinions of educated men on 

 these fundamental questions. At the beginning of the present 

 century it was the almost universal belief, that the earth had been 

 in existence some 5800 years, and the human race some six days 

 less. Now there are few men of ordinary education who do not 

 admit the great antiquity of man, and the vast age of the globe 

 which he inhabits ; while theologians vainly endeavour to persuade 

 us that the Mosaic six days meant six long geological period^, 

 forgetful that Moses (if indeed he was the author of Genesis) was 

 writing a history of the Jewish race and their beliefs, so far as he 

 could gather it from tradition, not a treatise on Geological Cos- 

 mogony. 



But just as a young man who has been subject to too great and 

 unwise restraint, when he has once broken the fetters, rushes into 



1 A study of Mr. Darmn's " Geological Observations," published first as early as 

 1844, will, I think, convince the most sceptical of the continued activity of the 

 volcanic forces in South America on a tremendous scale, which must leave some im- 

 pression on underground temperature there in future ages, though I agree with Prof. 

 Judd that there has not necessarily been the same actual display of energy at every 

 period of the Earth's history. This is dependent on many causes, which I hope to 

 be able to further explain at a future time. 



