R. D. Oldham — On Homotaxis and Contemporaneity 293 



II. — Essays on Speculative Geology. 



1. — On Homotaxis and Contemporaneity. 



By R. D. Oldham, A.E.S.M., 

 of the Geological Survey of India. 



IN any inquiry into the history of the earth as a whole, we are met 

 at the outset by a serious difficulty. In human affairs a general 

 view of history, not confined to a single country, would be practically 

 impossible, were we ignorant of the relations of the various eras 

 from which different races reckon their dates : thus, it would be 

 impossible to write a connected account of the history of Europe in 

 the classical period were it not possible to determine the relation of 

 the Olympian era to that dating from the foundation of the city of 

 Eome. Yet the supposed case is not unlike that to which the 

 geologist addresses himself when he endeavours to make a connected 

 survey of such widely-separated regions as Europe, India, Australia, 

 and America. 



In the supposed case of the Greek and Eoman eras, there are 

 numerous points of contact, principally dates of battles, which, 

 having been recorded by both nations according to their own system, 

 enable us to compare the two, and so to determine what would be the 

 date of any event, recorded by the one, had it been recorded by the 

 other. But in geology we have no such points of contact ; there is 

 a very general tendency to regard any two series of beds, in which 

 a few fossil forms specifically identical are found, as of contempora- 

 neous origin. That this view is erroneous, and that it would be 

 nearer the truth to say that two widely-separated beds, in which the 

 same forms are found, could not be of contemporaneous origin, was 

 long ago pointed out by Forbes and Huxley, the word homotaxis 

 being invented by the latter to express the relation existing. More 

 recently, at the Montreal meeting of the British Association, Dr. 

 Blanford went into the question at length, and fully showed how 

 erroneous is the assumption, often tacitly made, that similarity of 

 included organic remains indicates contemporaneity of origin of the 

 beds in which they are preserved. 



Be it understood that I am in no way desirous of depreciating the 

 value of palasontological evidence ; but, for the purpose of what may 

 be called historical geology, the merely approximate contemporaneity 

 indicated by homotaxis, however perfect, is by no means sufficient. 

 What we desire is something approaching to the accuracy of dates in 

 written history, rather than that vague "homotaxis" indicated by the 

 Stone or Bronze ages, with which we have to be satisfied in what is 

 known as the Pre- Historic period of human history. As long as we 

 are dealing only with the history of a single limited region, no serious 

 difficulty is likely to arise ; but when we try to bring the history of, 

 say, Australia and Europe, into relation with each other, a doubt may 

 well arise as to whether beds which would be classed as Lower Car- 

 boniferous if they occurred in Europe can be really considered as 

 of that age when measured by European standards. 



This is a question that palasontology alone can never answer 



