360 THE POPULAR SCIUNCPJ MONTHLY. 



Qaatrefages also speaks of the appearance of such varieties of men 

 as very probable. The care just mentioned as having been taken 

 of the malformation is all the more striking because the tail, as 

 has been shown in the European cases, is in sitting and riding no 

 very pleasant feature. They tell of canoes in the East Indies that 

 have holes made in the benches of the rowers. But it is not an 

 idle thought in this matter to sujjpose that the benches, like the 

 old German stools, were furnished with holes for ornament, or in 

 order that they might be more easily handled and disposed of, 

 and the incident can not be regarded as confirming the popular 

 legend. The result of these investigations is, as a whole, that a 

 formation, homologous even in outside appearance with an ani- 

 mal's tail, is originally present in the human foetus, and loses its 

 external characteristics at a later period of life through arrest of 

 growth, inversion, and waste. If these processes occasionally fail 

 to take place, the tail-feature is nevertheless not visible in the 

 grown man, and we can not draw from such malformations, even 

 if they appear frequently in a single race, any one-sided conclu- 

 sions respecting there having existed a former animal-like con- 

 dition. For it may be supposed with much more probability, 

 from the similarity of the forms in this feature of man and the 

 anthropoid apes, that their common ancestor had already shed 

 the external tail ; and hence that the 2:)rolongation of the chorda 

 in the embryo, wnth no vertebra contained in it, may be regarded 

 as a reminiscence of a still earlier ancestral form. 



A DISCUSSION in the International Geological Congress at "Wasliington, on cor- 

 relation of strata, was opened by Mr. G. K. Gilbert, of our Geological Survey, 

 who spoke first of local methods, where one rock lies upon another. Physical 

 continuity was a means of correlation, and perhaps the best method, but was sub- 

 ject to limitations. Traces were rarely possible for great distances. Indirect 

 methods must be resorted to. Beds of similar lithologic formation could be re- 

 garded as chronologically similar. Another method was the sequence with which 

 the deposits were laid. Layers following in sequence in different localities argued 

 the same conditions. There were limitations, however, to the use of both these 

 methods. Physical breaks afforded a fourth method of correlation, to which the 

 limitation would probably be distance. Simultaneous relations of bodies to some 

 physical event often afforded valuable evidence. Tliis method had been useful, 

 both at Salt Lake and on tlie Atlantic coast. Other aids in correlation were the 

 relation of deposits to some geological climate and the evidence of similar pliysical 

 changes. The similar action of gases in different beds showed chronological 

 similarity. This method was largely limited by local climatic changes, and gen- 

 erally the physical methods mentioned were all v.-duable at fhort range but of 

 little use at long range. The theoretical methods, in which floral and animal life 

 are called in, are perhaps more accurate. Of these are divergence from a status 

 at a fixed date, and the relations of the fauna contained in the deposits to cli- 

 mate. The value of a fossil species for purpose is dependent greatly on the length 

 of its life and the range of its space. Long life is a drawback, that makes the cor- 



