TRANSACTIONS OF SECTION C. 691 



Section C— GEOLOGY. 

 President of the Section.— W. T. Blanford, LL.D., F.R.S., Sec.G.S., F.R.G.S. 



THURSDAY, AUGUST 28. 



The President delivered the following Address : — 



In commencing an address to the Geological Section of the British Association on 

 the first occasion on which that hody has met outside of the British Islands I fed 

 much difficulty. Amongst the eminent geologists who have filled the post which you 

 have done me the honour of calling upon me to occupy for the present year there 

 are several who woidd have heen able, from their knowledge of both European and 

 American geology, to treat with authority of the many points of interest elicited by 

 comparison of geological phenomena on opposite sides of the Atlantic Ocean. My 

 own experience has been chiefly derived from the distant continent of Asia, and I 

 have not that intimate acquaintance with the geology of Europe, nor that know- 

 ledge_ of the progress of geological research in America, which would justify my 

 entering upon any comparison of the two continents. It has, however, occurred to 

 me that amongst the questions of wide importance connected with the correlation 

 of strata in distant parts of the world there is one to which some interesting con- 

 tributions have heen made by the w-ork of the Geological Survey of India, and hy 

 the geologists of Australia and South Africa ; and that a short time might be 

 profitably devoted to a consideration of a few remarkable exceptions to the rule 

 that similarity of faunas and floras in fossiliferous formations throughout the sur- 

 face of the world implies identity of geological age. 



It has probably occurred to other geologists here present, as it has to myself, to 

 he engaged in examining a country the geology of which was absolutely un- 

 known, and to feel the satisfaction that attends the first discovery of a character- 

 istic fossil form. A clue is at once afforded to the geology of the region ; one 

 horizon at least is believed to be determined, and from this horizon it is possible to 

 work upwards and downwards until others are found. 



It is, therefore, of especial importance to those engaged in geological exploration 

 to satisfy themselves whether the conclusion is correct that identity, or close specific 

 similarity, amongst fossil forms, is a proof that the heds containing them are of the 

 same geological age. It has been pointed out by some of the most careful thinkers, 

 and especially by Forbes and Huxley, that a species requires time to spread from 

 one area to another ; that, in numerous cases, a migratory specific form must 

 flourish in the region to which it has migrated, after it has died out in its original 

 birthplace ; and that the presence of the same species in two deposits at distant 

 localities may rather tend to indicate that both were not formed simultaneously. 

 Huxley, as is well known, invented the term ' hoinotaxis ' to express the relations 

 between such beds, and to avoid the possibly misleading expressions ' geological syn- 

 chronism,' and ' contemporaneous origin.' 



Despite such cautions, however, it still appears to be generally assumed hy 

 palaeontologists that similarity between faunas and floras is evidence of their belong- 

 ing to the same geological period; that the geological age of any formation, 

 whether marine, fresh-water, or subaerial, can be determined by a comparison of 

 its organic remains with those of other deposits, no matter how distaut/of which 



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