December 1, 1911] 



SCIENCE 



767 



quate conservation policy witli reference to the 

 harvesting of the native crop is immediately 

 imperative, and that it will also doubtless avail 

 more for the perpetuity of this resource than 

 any attempts at plantation methods. 



It is to be regretted that the author has not 

 considered in this connection the cost of the 

 operations, upon which must depend, of course, 

 the practicability of propagation. Since field 

 seeding seems impracticable, except under the 

 most extraordinary conditions, the procedure 

 must take the form of nursery methods, in- 

 volving considerable outlay in labor and equip- 

 ment. Without discussing the details, for 

 which space can not be taken here, it may 

 suffice to say that the cost involved in these 

 operations, computed on the basis of condi- 

 tions at Cedros, seems quite prohibitive. 



In conclusion, the admirable quality of this 

 contribution should be recognized. Though 

 lacking completeness in parts, as the author 

 himself admits, there are in this work, never- 

 theless, the abundant results of careful and 

 painstaking research. The magnitude of the 

 accomplishment is the more apparent to the 

 reviewer, as one familiar with the difficulties 

 and discouragements which beset its author 

 during the year upon the hacienda. 



J. E. KiRKWOOD 



Les syenites nepheliniques de I'Archipel de 

 Los et leurs mineraux. By A. Lacroix. Ex- 

 trait des nouvelles archives du Museum, 

 Series 5, Vol. III. Paris. 1911. 4to. Pp. 

 132, 10 plates and text illustrations. 

 In any work from the fertile pen of M. A. 

 Lacroix we are accustomed to expect the 

 thoroughness and accuracy that distinguish 

 the present petrographic study on the nephe- 

 linic syenites of the Isles of Los off the coast 

 of Guinea. This group of islands was ceded 

 to France by the Anglo-French convocation 

 of 1904. 



M. Lacroix signalizes the interesting fact 

 that the geological formations of the Guinea 

 coast difFer radically in their chemical com- 

 position from those of the nearby Isles of Los 

 (p. 8). In the nephelinic syenites constitu- 

 ting Rouma (Crawford) Island, lavenite and 



astrophyllite are constant constituents, often 

 present in as great quantity as Eegyrite, all 

 being distinguishable without the aid of the 

 microscope; sometimes one and sometimes 

 the other of these constituent minerals pre- 

 dominating. When these rocks contain ar- 

 fvedsonite, occasionally accompanied by a 

 little biotite, this amphibole forms crystals 

 which may attain a length of several centi- 

 meters. In addition to the elements above 

 noted, villiamite may also be found as well as 

 fluorite and pyrochlore, both in microscopic 

 quantities; more rarely eudialite is observable. 

 To them may be added several secondary 

 minerals. The author finds in the fact that 

 the lavenite is often formed after the feld- 

 spars a typical quality of these rocks, this con- 

 stituent being usually a primitive constituent 

 in rocks of this kind, although analogous con- 

 ditions have been observed in nephelinic 

 syenite from the Ord Range in Texas. 



The syenites of the Isles of Los are divided 

 by the author into the principal petrographic 

 groups, whose close relation to one another is 

 brought out by chemical examination. One 

 of them, more alkaline and containing little 

 or no lime or magnesia, is constituted by the 

 syenites with a?gyrite; the other, but a trifle 

 more calciferous, includes the syenites with 

 black amphibole and augite, and the alkaline 

 monzonites where plagioclase exists. 



The characteristics of these two groups and 

 those of the minerals found in the syenites 

 are very fully described. Among the minerals 

 found in the first group are the following: 

 feldspars, either sodium orthoclase (Rouma, 

 Kassa), or microcline (Rouma, Robane) ; 

 they especially abound in the pegmatites of 

 Rouma; nepheline occasionally occurring in 

 crystals five centimeters in length; sodalite, 

 a light yellow shade of this mineral, abounds 

 in the normal syenite of Rouma Island; in 

 the pegmatites the soldalite occurs in crystals 

 three centimeters long and of a light yellow, 

 or a lavender blue color, greenish in places, 

 jegyrite-acmite; the segyrite sometimes ap- 

 proaches to acmite, while in some specimens 

 of syenite from the northern part of Kassa 

 Island only acmite is found; asfredsonite, oc- 



