Geology and Mineralogy. 577 



Pliocene lavas were emitted under far quieter conditions and built 

 up the successive flows that formed the rhyolite plateau ; (5) that 

 during the many thousand years since the withdrawal of glacial 

 ice the Pliocene rhyolites Lave, since the beginning of Pleistocene 

 time, been steadily undergoing progressive changes, brought 

 about by the action of enormous volumes of superheated vadose 

 waters ; (6) that the gases contained in the thermal waters were 

 in great measure derived from vadose sources ; (7) that the erup- 

 tions and periodicity of geysers are phenomena due essentially 

 to varying conditions of reservoirs and channels of superheated 

 waters situated only short distances below the surface ; (8) that 

 the phenomena as seen to-day represent a phase in the evolution 

 of thermal springs. 



9. Tables for the Determination of 31inerals by means of 

 their Physical Properties, Occurrences, and Associates ; by 

 Edward H. Kraus and Walter F. Hunt. Pp. 254, New York, 

 1911 (McGraw-Hill Book Company). — The determination of 

 mineral species by means of their physical properties is particu- 

 larly useful in the instruction of the science, since it calls 

 the attention of the student to the characters with which it is 

 most important that he should become thoroughly familiar. The 

 tables of Weisbach, as translated into English by Frazer, have 

 been before the public for many years, serving a useful purpose 

 in many laboratories. We have now a new system of tables pre- 

 pared with much completeness and based primarily upon the 

 characters which appeal to the senses most directly : that is, 

 (1) luster, (2) color, then streak, hardness, cleavage, and specific 

 gravity. The fact that many minerals vary widely in color and 

 sometimes also in luster leads to their being introduced in a 

 variety of places in the successive tables ; this enlarges the work 

 considerably, but does not necessarily make the task of the 

 student more difficult. A useful feature of the work is the state- 

 ment of special characteristics and of associated species, which 

 is often important in the matter of identification. The work 

 opens with a concise explanation of physical properties and a 

 glossary of mineral terms. 



10. Composition of Struverite ; by R. C Wells (communi- 

 cated). — In the paper upon strilverite in the May number of this 

 Journal, pages 441 and 442, the formula Fe(Ta,Cb) 2 5 .6Ti0 2 

 should read FeO.(Ta,Cb) 2 O s .6Ti0 2 or expressed more simply 

 Fe(Ta,Cb) 2 (Ti0 3 ), 



Although it is stated on page 441 that "the analysis yields no 

 simple formula" a better statement would be that too much sig- 

 nificance should not be attached to the simple formula deduced 

 from the analysis, in view of the uncertainties of the analytical 

 methods. 



