Geology and Mineralogy. 69 



An interesting new mineral is sodium fluoride, which is called 

 villiaumite (after Villiaume, the collector of the material), which 

 occurs as one of the accessory constituents of the nephelite-syenite 

 in several places in the form of violet or carmine-red grains. It 

 is thought to be tetragonal ; cleavages good 001 and 100; double 

 refraction almost wanting, but is negative ; index 1*328, less than 

 that of water and smallest of known minerals ; hardness 2—2*5 ; 

 specific gravity 2*8. It has in thick sections pleochroism in the 

 red variety. Is soluble in water. 



The name of losite is given to a mineral whose properties are 

 much like those of cancrinite, from which it differs, however, in 

 several particulars, notably in lesser birefringence (*001-*012). 

 Material could not be obtained for chemical investigation. 



In addition to those mentioned, other interesting rare minerals 

 found in these rocks are astrophyllite, rinkite, wohlerite, eudialyte, 

 catapleiite and pyrochlore. 



Lacroix contrasts these rocks with those which constitute the 

 adjoining coast, and which he describes as hypersthene granites 

 (charnockite) and norite of the Ivory Coast, and gabbros and 

 peridotites (wehrlite and dunite) of French Guinea. He finds 

 that the analyses of the wehrlite and dunite prove them to fall in 

 unnamed sections of the Quantitative Classification and he pro- 

 poses for the former the designation kakoulimose (V, 1 (4), 1 (1), 

 2) and for the latter gaineose (V, 1 (5), 1 (1), 2). 



The memoir contains a considerable number of analyses and is 

 an important addition to our knowledge of the alkalic rocks. 

 The fine plates show many interesting petrographic details. As 

 no associated rocks, or strata, are known, the occurrences add 

 nothing at present to our knowledge of the origin of such rocks, 

 or to their geological age. l. v. p. 



13. Potash in the United States. — The efforts being made to 

 find a supply of potash in this country are detailed in an advance 

 chapter by Hoyt S. Gale from the Contributions to Economic 

 Geology. The work of Gilbert and Russell showed reasonable 

 ground for the theory that concentrated beds of workable and 

 commercially valuable salines may exist in the strata underlying 

 the Great Basin deserts. Accordingly work at Fallon, in northern 

 Nevada, was begun on October 6 ; on December 1 the well was 

 360 feet deep, and it is expected that drilling will be continued 

 until a depth of at least 1,000 feet is reached. The author adds 

 that " There is a good possibility that deposits of the Stassfurt 

 type exist in the United States. Probably the only feasible 

 method of exploring for such deposits is by drilling. The work 

 at Fallon is now fairly started but is no more than a beginning on 

 the project as a whole. It is well that the work should proceed 

 cautiously at the start, as little is to be gained by hasty or ill- 

 considered expenditure. Experience gained in the preliminary 

 tests now under way should help to make each succeeding test 

 more effectual. It is to be hoped that the project already under- 

 taken will be carried to a satisfactory conclusion, and if this is to 



