Page:Popular Science Monthly Volume 40.djvu/374

Quatrefages 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 suppose 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 animal's tail, is originally present in the human fœtus, 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 conclusions respecting there having existed a former animal-like condition. 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 prolongation of the chorda in the embryo, with no vertebra contained in it, may be regarded as a reminiscence of a still earlier ancestral form.

 

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A discussion in the International Geological Congress at Washington, on correlation 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 subject to limitations. Traces were rarely possible for great distances. Indirect methods must be resorted to. Beds of similar lithologic formation could be regarded 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. This method had been useful, both at Salt Lake and on the Atlantic coast. Other aids in correlation were the relation of deposits to some geological climate and the evidence of similar physical changes. The similar action of gases in different beds showed chronological similarity. This method was largely limited by local climatic changes, and generally the physical methods mentioned were all valuable at short 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 climate. 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-