Geology. 371 



Owing to difficult conditions precluding proof reading, various 

 typographical errors appear in this Bulletin. These should 

 occasion no great inconvenience in its use. They are seldom 

 serious and may readily be excused in this period of nearly 

 universal war. It must be held very creditable to the Mexican 

 Survey to bring out the work at all. May it not be recalled that 

 our own civil war delayed Newberry's record of the San Juan 

 expedition nearly seventeen years '? a. K. w. 



2. Isostasy in the Ligld of the I'lanetesimal Theory; by T. 

 C. Chamberlin. [Note to the Editors of this Journal.] — In the 

 August number of this Journal, " C. S." does me the honor to 

 give an excellent notice of my recent little book on " The Origin 

 of the Earth." There is one sentence in the notice which, though 

 not inaccurate when critically read, will, I fear, give to many 

 readers an erroneous impression, and as the subject to which it 

 relates is one of much importance I beg to add a word to fore- 

 stall misapprehension. After referring to the view advanced in 

 ihe book that the earth is segmented into heavy stiff sub-oceanic 

 cones between which lie more irregular, weaker and lighter con- 

 tinental wedges, and that at times of diastrophism these move 

 upon one another along "yield tracts," the review says : "This 

 hypothesis seems to be diametrically opposed to the working 

 hypothesis of isoslasy and the latter's postulate that the lelief of 

 the earth's surface is compensated for by corresponding varia- 

 tions in surface density which cease at a depth equal to a fiftieth 

 or a hundredth part of the radius of the earth." 



It is true that the hypothesis that I have offered departs radi- 

 cally from the interpretation of the mode by which isostasy is 

 secured and is at variance with certain limitations that have been 

 assigned the distribution of density in the outer part of the earth 

 which are not thought to have a secure basis, but the view 

 advanced in my book, far from being diametrically opposed to 

 demonstrated or theoretically essential elements of isostasy, ex- 

 presses its good will toward the doctrine by offering, on its own 

 part, anew view of the mode by which such approximate isostasy 

 as exists is secured. This new view is consistent with the grow- 

 ing evidence of a high state of rigidity in the earth. It also 

 postulates an adequate cause for the initiation and maintenance 

 of isostasy through all the geologic ages with an effective residue 

 operative at the present time. In short, the new view endeavors 

 to meet on broad, adequate and lasting grounds what are regarded 

 as the weak points in the doctrine of isostasy as it has heretofore 

 been advocated. The limitations of differences of density in 

 depth are not regarded as having any trustworthy basis, and this 

 view is supported by competent mathematical investigation, the 

 results of which will appear in time. The purpose of this note 

 will be accomplished, if it makes clear that the book in question 

 offers a new line of support for the general doctrine of isostasy 

 and is at variance with current views only on points in respect to 

 which these views are held by some careful students to be weak. 



University of Chicago. 





