Geology. 4:->7 



eminent scientists. For example, we find: Bjercknes, Clerc Max- 

 well, llelmholz, INIolda, Michaelson, Rhumkorff, etc. n. s u. 



8. A Text- Book of Physics, Fourth Edition; edited by A. 

 VV. Duff. Pp. xiv, 692 ; 609 figures and 279 problems. Phila- 

 delphia, 1916 (P. Blakiston's Son & Co.). — A careful comparison 

 of the latest edition of this work with the third (see vol. xxxiv, 

 page 483) shows that the text has been thoroughly revised. The 

 method of presentation has been simplified and clarified in many 

 places, especially in the paragraphs relating to the dynamics of 

 rotation. The symbolization lias also been improved ; for exam- 

 ple, u is replaced by v Q in the case of initial velocity. A new 

 part on Sound has been written, especial attention being paid to 

 the recent investigations of Miller, Sabine, and others. Typo- 

 graphical errors have been eliminated as far as possible. It is 

 thus evident that the fourth edition shows appreciable improve- 

 ment over the third and that it is a thoroughly reliable and well- 

 balanced text-book. n. s u. 



II. Gkology. 



]. Expedition to the Baltic provinces of Russia and Scandi- 

 navia, 191Jf. Part 1. — The correlation of the Ordovician strata 

 of the Baltic basin with those of eastern North America ; by 

 Pekcy E. Raymond. Bull. Museum Comp. Zoology, vol. lvi, 

 No. 3, Shaler Memorial Series No. 2, 1916, pp. 179-286, pis. 1-8. 

 Part 2. — The Silurian and high Ordovician strata of Esthonia, 

 Russia and their faunas; and Part 3.'— An interrelation of the 

 Silurian section of Gotland ; by VV. IT. Twenhofel. Ibid., 

 vol. lvi, No. 4, Shaler Memorial Series No. 3, 1916, pp. 289-354, 

 pis. 1-5, text fig. 1. — These important and far-reaching correlation 

 papers comparing the Ordovician and Silurian of Esthonia, 

 Sweden, and Norway with those of North America, give much 

 more detail than any others in the English language. The 

 Ordovician begins with the Dictyonema beds, for earlier there 

 had been elevation (warping) and erosion throughout the area 

 studied. The formations which immediately succeed the basal 

 ones are correlated by Raymond with the American Beeknian- 

 town, and in this he is in harmony with the European strati- 

 graphers, but differs from the conclusions of some American 

 geologists. In correlation, Raymond places main reliance on the 

 graptolites, though he remarks, "If there were no other evidence 

 than that afforded by the time of the first appearance of certain 

 genera in Russia and America, it might well happen that the 

 Walchow and Kunda formations [the basal Ordovician of Estho- 

 nia] might be correlated with the Chazy, but I do not see that 

 they could be correlated with any younger strata" (268). Since 

 the reviewer's visit to Esthonia in 1903, it has always seemed to 

 him that the faunal development of these formations, especially as 

 shown in the brachiopods, was rather that of the Chazy than the 



Am. Jour. Sci. — Fourth Series, Vol. XLIT, No. 251. — November, 1916. 

 30 



