Geology. 529 



further states that a bipedal animal never could or did develop a 

 patagium without giving up bipedalism. • This makes it some- 

 what difficult to account for the pre- and post-patagia 

 of modern birds, which are usually looked upon as vestigial 

 organs. One important conclusion is that the birds and ptero- 

 dactyls are unrelated, the similarities which they exhibit being 

 merely the result of convergence, while the dinosaurs and birds 

 show many striking similarities which indicate parallel adapta- 

 tions in forms having a common ancestry. e. s. l. 



7. Trait'e cle Geologic I, Les Phenomenes geologiques / par 

 Emile Haug. Pp. 538, 8°, 195 figs, and 71 pis. Colin, Paris 

 1907. — This large work is a general treatise on geology, of the 

 type of those of Suess and Neumayr; the volume corresponds in a 

 general way with the first one of Charnberlin and Salisbury, 

 being devoted to geological processes ; it thus gives a general 

 presentation of the subject of dynamical geology. It has the 

 descriptive character of Neumayr's volumes rather than the 

 philosophical nature of the American work just mentioned. In 

 so far as the theoretical treatment of subjects is involved, the 

 author naturally reflects the views of the French school. It is 

 well and clearly written, the material has been selected with 

 judgment, the author exercises an admirable restraint and poise 

 in his presentation of a topic, so that, the balance between 

 descriptive matter and theory being justly held, it is an excellent 

 work for the reader who desires a general knowledge of the sub- 

 ject. In this respect the work recalls the text-book of Geikie. 

 A valuable feature is a short bibliography appended to the dis- 

 cussion of each important topic, giving the chief works relating 

 to it. The cuts and diagrams are well selected, and the half-tone 

 plates are reproductions of remarkably good photographs, which 

 show, as a rule, very clearly the phenomena which they are 

 intended to depict. One of the greatest advances, if not the 

 greatest, that has been made during the past five years or so in 

 geological text-book making, is in the quality of pictorial illus- 

 tration, and in this respect the work is up to the recent standard. 

 While intended as a work of reference, and for reading by 

 advanced students in France, the volume is one that commends 

 itself to every geologist, and should be in every geological 

 library. l. v. p. 



8. Key for the Determination of the Rock-forming Minerals 

 in Thin Sections y by A. Johannsen - . Pp. 542, 8°, 1 col. pi. New 

 York, 1908 (Wiley & Sons). — Perhaps no more striking evidence 

 could be given of the extent to which the study of rocks in thin 

 sections has become a science in itself, than the appearance of 

 this large volume entirely devoted to technical methods for 

 determining rock minerals by optical methods. While not a text- 

 book, the first part, comprising some forty odd pages, is given to 

 a brief explanation of the phenomena of polarized light, the 

 optical properties of crystals, and the methods for their observa- 

 tion and determination. In a second part of about the same 



