1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 109 



II. 



in. 



IV. 



Si0 2 .. 

 M;;0 ... 

 CaO ... 

 AI2O3 - . 

 Fe 2 Os.- 

 FeO ... 

 MnO ... 



S( >, 



Ignition 



Per cent 



51. 4:. 



18.43 



24. 02 



2.91 



1.(16 



. 96 



trace. 



trace. 



1.08 



Per cent. 

 40.23 



89.46 



2. is' 



4 02 

 trace 



54. 215 



19. 82 



J I. 7! 



. 59 



.2(1 



.27 



Perci a/. 

 12 38 

 42. 14 



.117 

 .97 

 .17 



99. 94 



I. The gray pyroxene. II. The green serpentine resulting from its 

 alteration. III. White pyroxene, and IV, the yellow serpentine re- 

 sulting from its alteration * 



The changes whieli are shown to have taken place are self-evident 

 and need not be commented upon. The fact that no free silica or sec- 

 ondary silicates other than serpentine are found in the sections may be 

 due to the entire removal of the excess silica in the pyroxene, as was 

 the case with the calcite, or as seems very probable, the inclosing dolo- 

 mite may also have been acted upon and yielded sufficient magnesia to 

 convert the whole into serpentine as suggested by Daunt in the case 

 of the serpentine and dolomite of Westchester County, X. Y. In their 

 high percentages of water it will be observed these serpentines approach 

 closely to the so-called retiualite variety as given by'Daua.f The ex- 

 treme compactness and homogeneity of the Montville stone, however, will 

 scarcely permit us to consider it as a mixture of deweylite and serpen- 

 tine as suggested by Professor Dana in the case of the retiualite of Gren- 

 ville, Canada. Secondary minerals other than serpentine and calcite 

 are, however, by no means wholly lacking. In many cases the granules 

 of the light yellow serpentine (No. iv of analysis) are bordered by a 

 finely microcrystalline, creamy white, somewhat chalky looking mineral, 

 which I have not been able as yet to obtain in sufficient purity for ac- 

 curate determination, but which is judged to be a mixture of calcite and 

 magnesite. Aside from this are occasional aggregates of a white color, 

 and with a compact microgranular or short fibrous structure which 

 under the microscope are seen to consist of a dense aggregate of minute 

 calcite granules associated with numerous elongated silky fibers scarcely 

 affecting polarized light but giving extinctions always parallel with 

 their greatest elongation. The entire mixture submitted to Mr. Catlett 

 for analysis yielded results showing it to consist of 90.17 per cent, 

 mixed carbonates of lime and magnesia (mostly lime) and 9.07 per cent. 

 of a mineral having essentially the composition of serpentine with traces 

 of iron oxides, alumina, soda, and potash. It is evident that the fibrous 



* Analysis of serpentine from this same locality, as given by Dana (System of 

 Mineralogy p. 467) is as follows: Si0 2 4-2.5; MgO 42.16; H : 14.22; FeO 1.96. This, 

 it will be noted, agrees almost exactly with the above No. IV. 



t Am. Jour. Sci., July, 1880, p. 32. 



t System of Min., p. 467. 



