632 



SCIENCE. 



[N. S. Vol. XXIII. No. 590. 



the Cretaceous peneplain — Coot Hill, for ex- 

 ample, itself consisting of hard granite-gneiss, 

 fronts Lake Champlain with an almost pre- 

 cipitous escarpment 1,200 or 1,400 feet above 

 the flat Ordovician, Beekmantown limestone, 

 which abuts sharply against its base. There 

 is surely a great fault between the two and 

 the question arises is the relief due in large 

 part to a fault-scarp not yet obliterated or 

 did the ice-sheet take away 1,200-1,400 feet of 

 Chazy, Trenton and Utica strata which must 

 otherwise have stretched eastward from it? 

 Or again, did some pre-glacial river aid in 

 the work? My own disposition is to place 

 confidence in faulting of date since the Cre- 

 taceous and not yet obliterated. 



I have never been able to establish post- 

 glacial faulting either by dislocated drift or 

 broken glacial strise, although both possibilities 

 have been kept in mind. 



As Professor Davis states, the graben-like 

 valleys do run usually with the general struc- 

 tural trend, but there are occasional ones 

 which strike across this direction. The 

 valley of the Cascade lakes, shown in Fig. 7 

 of my paper, is such an one (Popular Science 

 Monthly, March, 1906). The sides are quite 

 steep and lofty and the lakes are almost 

 at the crest of a divide. A similar cross- 

 canyon lies just north. The little cross-valleys 

 mentioned on p. 201 have similar relations. 



On p. 203, the fifth line from the bottom, 

 ' Needles ' should read ' Noses.' The old New 

 York name for this uplift is the ' Noses.' 

 J. F. Kemp. 



Columbia University. 



vabiation versus mutation. 

 The suggestion of weakness in the mutation 

 theory of evolution given by Dr. Merriam in 

 a recent number of this journal, from evi- 

 dence afforded by living faunas as affected 

 by geographic environment, contrasts greatly 

 with apparent evidence in favor of the muta- 

 tion theory advanced by Professor White in 

 the preceding volume. Both are able exposi- 

 tions, but from very different standpoints, the 

 one from living evidence, the other from such 

 information and rational inferences as we 

 have been able to derive from paleontology. 



The facts in both instances are well known, 

 for no biologist could for a moment deny that 

 geographic isolation plays an important part 

 in modifying and frequently originating spe- 

 cies, though to a wonderfully variable extent, 

 some forms remaining constant throughout 

 very extended ranges, while others are much 

 more plastic, giving rise to species or sub- 

 species in almost every large mountain valley. 

 The change wrought in many winged Cole- 

 optera when established on oceanic islands is 

 frequently alluded to, the wings becoming 

 aborted and other modifications supervening 

 which eventually give rise to what must be 

 considered distinct species. 



At the same time we must admit that spe- 

 cies are succeeded by other species in succes- 

 sive strata of a geological formation, with 

 such abruptness and frequently with such 

 marked divergencies, as to preclude the idea 

 that the modifications could be brought about 

 by simple changes of climate. It would ap- 

 pear that something else has affected the 

 stability of species to give rise to these ob- 

 served facts, and, as the development of spe- 

 cies by mutation has proved to be at least 

 possible, this seems at present to be the most 

 plausible hypothesis in many instances. A 

 so-called sport is much more difficult to com- 

 prehend than any modification brought about 

 by visible alteration of environment, and is 

 probably caused by some let-up in the multi- 

 tude of environmental conditions that hedge 

 about a species in nature and cause it to 

 maintain its constancy. There is no reason 

 to assume that if this sudden change in the 

 surrounding conditions should be maintained 

 the sport might become a firmly established 

 species, and this mode of evolution seems, 

 from paleontological evidence, to have become 

 much more universal at certain epochs of the 

 earth's history than at others. 



In other words, there is probably much 

 truth in both the hypotheses that have been 

 advanced to account for evolution, and it 

 seems to me that Dr. Merriam condemns the 

 mutation theory much too sweepingly — there 

 may be a good deal in it. 



Thos. L. Casey. 



St. Louis, Mo. 



