Geology and Mineralogy . 359 



lation in its varied phases is then treated, and this leads to the 

 subject of differentiation. Magmas formed by assimilation (syn- 

 tectics) may be split or differentiate and thus give rise to 

 various types of igneous rocks. The process as it occurs in masses 

 of various modes of occurrence is described, and is followed by 

 a discussion of the theory of volcanic action in the central vents. 

 The next chapter summarizes the author's general theory as to 

 the origin of igneous rocks which is called the " eclectic " one, 

 since it includes the ideas of many other petrologists. In a 

 general way it is somewhat similar to the one propounded by 

 Loewinson-Lessing, but differs in some important respects. The 

 author then states a provisional genetic classification of magmas 

 derived from considerations previously stated. 



The last part of the work is devoted to a discussion of the dif- 

 ferent rock clans, of their relations, occurrences, and genetic 

 derivation, and the work closes with several appendices giving 

 the data upon which a number of conclusions have been reached. 

 The work is clearly written and amply illustrated, and shows the 

 evidence of a great amount of work in the examination of the 

 literature and collating of material, and in field studies. Whether 

 he may agree with all of the views here set forth by Professor 

 Daly, or not, it is a work which should be read by every petrolo- 

 gist, as his interest in this subject cannot fail to be stimulated by 

 the broad treatment of the subject matter and the enthusiasm for 

 his ideas which is everywhere evinced by the author. L. v. p. 



17. Bergalite. — A new variety of the basaltic rocks carrying 

 melilite, from the Kaiserstuhl in Baden. This group of much dis- 

 sected volcanoes consists of various alkalic types of magmas in 

 flows, dikes, etc. The present rock occurs in a few small dikes, 

 and when unaltered has a black somewhat pitchy appearance. 

 In thin section it is seen to consist of phenocrysts of hatiynite, 

 apatite, perofskite, melilite, and magnetite, in a groundmass of 

 melilite, hatiynite, nephelite, biotite, perofskite, magnetite, and 

 brown glass. Carbonates and zeolites are present from altera- 

 tion. The melilites afford excellent material for the study of 

 this mineral, especially the peg-structure, and the author con- 

 cludes that this is not due to inclusions of glass, or other sub- 

 stances, but is a process of alteration into another mineral, to 

 which the name of Deeckeite is given. It was found that the 

 peg substance was insoluble in strong hydrochloric acid which 

 permitted sufficient material for an analysis to be obtained on 

 dissolving the other constituents. From the analysis the formula 

 (HKNa) a (Mg0a)(AlFe) a (Si,O 6 ) 6 + 9H 2 was derived, which sug- 

 gests that it is a zeolite near ptilolite and mordenite in compo- 

 sition. 



The analysis of the rock shows it to be of a very basic nature, 

 as follows: 



Si0 2 A1 2 3 Fe 2 3 FeO MgO CaO Na 2 K 2 H 2 C0 2 Eest 

 33-03 13-02 4-73 5-60 3'97 12-72 5-79 3-04 6-00 8-42 4-20 = 100-52 



