TRANSACTIONS OF SECTION C. 



691 



Section C— GEOLOGY. 

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



TlirilSDAY, AUGUST 28. 



The Pkesident cU'livcred the foUowiiif^ Addross : — 



In commenclnf^ an ad<lress to the Geological Section of tlio British As.soci;;tion on 

 tiie lir.vt occasion on wliicii that body has met out.side o{ tlie British Islands I feel 

 much (lilliculty. Amongst tlie eminent geologists who have filled the po.st which you 

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

 are s(^veral who would liave been able, from their knowledge of both J"iUro])ean and 

 Anu'vican geology, to treat with authority of the many points of interest elicited by 

 rnmiiarison of geological plienomena on opposite sides of the Atlantic Ocean. My 

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

 hiive not that intimate acquaintance witli the geology of Europe, nor that know- 

 It'dge of the progress of geological researcli in America, which would justify my 

 entering upon any comparison of the two continents. It has, however, occurred 1o 

 nu; that amongst the questions of wide importance connected with the correlation 

 of strata in distant parts of tlie woi'M there is one to which some interesting con- 

 tributions have been made by the work of the Geological Survey of India, and by 

 the geologists of Australia and South Africa ; atid tliat a short time might bo 

 protitably devoted to a consideration cif a ffw remarkabh; 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 iiere present, as it, has to n^yself, to 

 be engaged in examining a country the geology of whicli was absolutely mi- 

 known, and to feel tlie satisfaction tliat attends tins first discovery of a cliaracter- 

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

 horizon at least is believed to be detennincd, and tVom this horizim it is possible to 

 work upwards and downwards until others are found. 



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

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

 similarity, amongst fossil forms, is a proof that the beds containing tiiem 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 sjiread from 

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

 flourisli in the resrion to which it has mign-ated, after it has died out in its original 

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

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

 iluxley, as is well known, invented the terra 'homotaxis ' to ex])ress the relations 

 between such beds, and to avoid th(i possibly misleading expressions ' geological syn- 

 chronism,' and ' contemporaneous origin.' 



Despite such cautions, however, it still appears to be generally ass^inied by 

 paknoontologists that similarity between faunas and floras is evidence of tlleir 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 distant, of wbidi 



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