498 



SCIENCE 



[N. S. Vol. XLIV. No. 1136 



of a method of procedure which may be well 

 known to photographers by the fact that it 

 appears to be unknown to nearly all of the 

 working geologists and zoologists with whom 

 it has been discussed. 



The utilization of the swing-back to elimi- 

 nate distortion in the photographs of high 

 buildings has long been known; the subject 

 of this note is the application of the same 

 method to increasing the depth of focus where 

 both foreground and distance are desired, the 

 swing-back being so manipulated as to in- 

 crease the distance between the lens and the 

 foreground portion of the photographic sur- 

 face and to lessen the distance to the back- 

 ground portion of the same. The method is 

 of course inapplicable where the objects in 

 the foreground are high, and the element of 

 distortion might bar it for some pictures, but 

 useful applications of the method are many 

 and will occur to all. 



Lancaster D. Burling 



Ottawa, Canada 



SCIENTIFIC BOOKS 



Grundlagen und Methoden der Paleogeog- 

 raphie. Fundamental Problems and Meth- 

 ods of Paleogeography. By Dr. Edgar 

 Dacque, Privatdozent an der Universitat 

 Miinchen. Gustav Fischer, Jena, 1915. 

 Dacque's notable work is a comprehensive 

 review of the literature of paleogeography and 

 of the opinions of many geologists, represent- 

 ing German, Austrian, French, English, 

 American, Swedish, Norwegian, Dutch and 

 Italian thought, regarding the problems of the 

 science. The list of authors cited comprises 

 nearly five hundred names. The citations are 

 so arranged that the views of any thinker on 

 a specific problem are stated in appropriate 

 context with those of others who may or may 

 not agree with him. For the most part they 

 are abstracts or interpretations, but Dacque's 

 presentation is accurate and impartial to a 

 degree which may even seem lacking in dis- 

 crimination, since speculations and respectable 

 theories are treated with similar considera- 

 tion. There is, however, a certain justifica- 

 tion for this attitude, paleontology being in a 



very speculative stage of development and its 

 problems being open to various tentative solu- 

 tions. The work having been prepared for 

 courses of lectures given at the University of 

 Munich in 1912-13 and 1913-14 is marked 

 by a didactic character. The advanced student 

 will therefore find in this comprehensive re- 

 view much that may seem elementary; he will 

 also find much that is suggestive and helpful. 



The chief value of the work for American 

 readers lies in the numerous references to for- 

 eign writers and to views which are given 

 more serious consideration by European geol- 

 ogists than they commonly are among Ameri- 

 cans. In so far as American thought has been 

 influenced by Chamberlin's far-reaching and 

 fundamental studies, it has abandoned some 

 theories to which Dacque gives credit and has 

 advanced to concepts which he does not dis- 

 cuss. 



The introduction and the history of the 

 literature of paleogeography for the past 

 thirty-five years occupy the first forty pages 

 of the work, and are followed by a discussion 

 of the surface and structure of the earth. 

 The statement includes the tetrahedral theory, 

 as well as the disruption of the moon from the 

 earth on the site of the Pacific Ocean, and 

 closes with a consideration of the constitution 

 of the earth on the assumption that the 

 spheroid consists of a core of nickel iron sepa- 

 rated from the known lithosphere by a zone of 

 molten, yet rigid, magma, which allows hori- 

 zontal displacements of the crust to occur. 

 There is a certain parallelism with Barrel's 

 hypothesis of an asthenosphere or zone of 

 weakness, but German speculation suggests 

 the possibility of horizontal movements of the 

 outer crust far in excess of any that have been 

 postulated by American investigators. Thus 

 Dacque discusses, as being within the range 

 of credible hypothesis, wanderings of the pole 

 amounting to twenty-five degrees of latitude 

 and the even greater displacements of the 

 continental masses postulated by Wegener. 



Changes in the position of the pole might 

 occur through absolute change in the position 

 of the earth's entire mass with reference to 

 the axis of rotation, or through relative move- 



