Status of the Theory of Isostasy. 317 



Hayford. Its points, however, seem to the writer poorly 

 taken. The statements are mostly general, there is an 

 absence of demonstration, and the whole article serves 

 more to befog than to' elucidate the subject. It would 

 hardly be necessary to review this paper were it not 

 for the fact that it was published in a leading geo- 

 logical journal and was written by a mathematician for 

 geologists. 



MacMillan concedes in the introductory statement that 

 the geodetic data have placed "the hypothesis of isos- 

 tasy upon a solid foundation of credibility, ' ' but con- 

 siders that it is not proved and "that with a slight 

 modification of the hypothesis the ' depth of compensa- 

 tion' could be made to retreat to the center of the earth 

 or vanish altogether. ' ' 



The concluding paragraph of his article states : 



" While the theory of isostasy has made a very successful 

 approach to the solution of the problem of bringing the anomalies 

 of observation into accord with the theory of gravity, it must be 

 admitted that there is no evidence to show that the solution of 

 the problem is necessarily isostatic. ' ' 



MacMillan does not offer any non-isostatic solution, or 

 even constructive criticism, but dwells on the fact that 

 changes of assumption in regard to the distribution of 

 compensation give different depths of compensation, and 

 that an infinite number of solutions could be made. 



MacMillan is apparently unaware of the existence of 

 other analyses of Hayford and Bowie's work, even of 

 those published in the same journal as his article. For 

 example, he makes, as though they were new discoveries, 

 some general adverse comments on Hayford's interpre- 

 tation of gravity anomalies in terms of thickness of 

 rock, 24 although the writer had discussed this topic 

 specifically and in varied related aspects. 25 MacMillan's 

 article in fact suggests a rather superficial knowledge 

 even of Hayford 's work. Two general topics which he 

 discusses as involving fundamental errors it will be 

 necessary to amplify here under separate topics in 

 order to show what are the difficulties and to what degree 

 they affect the conception of isostasy. In both cases 

 there is found to be no basis for his criticisms. 



24 W. D. MacMillan, op. cit., pp. 110, 111. 



25 Joseph Barrell, op. cit., pp. 297-301; also parts IV and V, pp. 289-314, 

 441-468, 537-555. 



