v " Scientific Intelligence. 



information. In the very nature of the case, this chapter is rather 

 dry, while the next five chapters, whioh deal with the pure physios 

 of colloidal phenomena, are very interesting both on account of 

 the subjeot matter itself and also because of the olearness of pre- 

 sentation. Afore specifically, these chapters deal with the ultra- 

 microscope, the phenomena and theory of Brownian motion, the 

 optical properties of colloidal solutions, the determination of the 

 size of ultramicrosoopic particles, and the motion of colloidal par- 

 ticles in the electric field. The titles of the eighth, ninth and 

 tenth chapters are respectively : "The Coagulation of Colloids," 

 " Theory of the Stability of Colloids," and " Practical Applica- 

 tions of the Study of Colloidal Solutions." This last chapter is 

 also very useful since it deals with various manufacturing pro- 

 cesses, dyeing, purification of effluent waters, agriculture, and 

 physiological applications. 



The value of the monograph is increased by the presence at the 

 end of each chapter of a long list of bibliographical references. 

 Since the important subject of colloidal solutions is often neg- 

 lected this compact and excellent text should be welcomed by 

 advanced students and teachers of physics. h. s. u. 



II. Geology and Natural History. 



1. Stratigraphy and fauna of the Tejon Eocene of Califor- 

 nia ; by Roy E. Dickerson. Univ. California Pub., Bull. Dept. 

 Geology, vol. ix, No. 17, 1916, pp. 363-524, pis. 36-46, text figs. 

 1-14. — This valuable work has far-reaching import in that it 

 stratigraphically and faunally establishes the Tejon formation in 

 its variable development throughout California. The Tejon, 

 although a thick formation, is a faunal unit, and unconformably 

 overlies the basal Eocene, the Martinez ; it in turn is usuall}' 

 unconformably overlain by the Oligocane. The fauna consists of 

 about 300 species and many range throughout the series. Not 

 more than four forms pass into the Oligocene and but 25 are 

 derived from the Martinez. The Tejon is divided into four 

 faunal zones and their distribution is shown on paleogeographic 

 maps ; the youngest zone has widest distribution when the Pacific 

 Ocean lapped the base of the Sierra Nevadas, depositing here the 

 lone formation and its equivalent, the auriferous stream and 

 bench gravel* of the Sierra Nevadas. The Eocene closed with 

 extensive deposits of rhyolitic ash and mud flows, followed by 

 andesitic tuffs, lavas, and mud flows. 



The Tejon fauna is partly a descendant of the earlier Martinez, 

 to which were added many migrants from the Gulf of Mexico by 

 way of the Panama or Tehuantepec portals, though less than 20 

 species, or about 1 per cent, are common to the two realms. The 

 relationship of the Tejon is with the Midway, Wilcox, and Clai- 

 borne of the Gulf of Mexico area, but more decidedly with the 

 last, while the Martinez appears to be older than anything in 

 the Tertiary of the Atlantic area. c. s. 



