MINERALOGY AND PETROGRAPHY.^ 
Petrographical News.— The serpentine of Montville, 
N. J., occurs in veins and as isolated nodules in crystalline 
dolomite, and also as a thin coating on irregularly rounded 
masses of a gray crystalline pyroxene, with the chemical and 
optical properties of diopside. The examination of thin sec- 
tions across the contact between the enclosing serpentine and 
its nucleus of pyroxene shows conclusively that the former is 
the direct product of alteration of the latter. In almost all 
cases the resulting serpentine is found to be slickensided and 
grooved as if it had been shoved along against some hard sub- 
stance, and had thereby suffered planing. The origin of the 
pressure producing this shoving is thought by Mr. MerrilP to 
be the increase in volume which the pyroxene undergoes in its 
change to serpentine. Even when the alteration is complete 
and no trace of the original pyroxene remains, the origin of the 
serpentine through the hydration of some magnesium mineral 
is shown by the crowding of the calcite grains associated with 
the serpentine into broad fan-shaped masses. Analyses of the 
pyroxene core and serpentine surrounding it substantiate the 
conclusions reached by the microscopic study of thin sections. 
SiO, MgO CaO. AlA FeA FeO Ign. 
Pyroxene 54.22 19.82 24.71 .59 .20 .27 -14 
Serpentine 42.38 42.14 -OZ -97 -^7 ^4-i2 
From the fact that no veins of quartz are to be found in the 
serpentine, it is thought that sufficient magnesium was fur- 
nished by the dolomite to change all of the silica of the py- 
roxene into serpentine.— The ophiolite from Thurman, Warren 
Co., N. Y., is observed by the same author' to have originated 
in the same manner as the serpentine from Montville. In this 
case, however, the original pyroxene occurs in little grains and 
concretionary masses scattered through calcite. — The rocks to 
the north of Lake Bolsena in Italy consist principally of trach- 
ytes, according to Klein,* and those to the south of a leucite 
bearing series. The former include olivinitic and non-olivmitic 
;n different members which the amount of plagio- 
es largely. The leucite rocks embrace tephntes, 
and leucitophyres. The first two contain porphy- 
' Proc. U. S. Nat. Mui 
•' Amer. Jour. Sci. March. l8& 
' Neue Jahrb f. Min. , etc., B. 
, Bayley, Colby ITni 
