PENNER, THE WATCHUNG BASALT 101 



Between the glassy crusts and the holocrystalline interior, transitions of 

 €rystal-developnient produce aphanitic phases. 



The crusts frequently present a shattered appearance due to the sudden 

 chill which they experienced, and at times pockets among the bowlders 

 are filled with considerable masses of breccia of this nature. This was 

 probably originally a usual feature, but, as will appear presently, such 

 pockets of glass were, for several reasons, peculiarly subject to the action 

 of the processes which formed the secondary minerals. 



The chemical composition of the basalt is shown in the following 



analyses of typical examples :^^ 



I II III IV 



SiOo 51.78 51.36 51.82 50.19 



ALO3 12.79 16.25 14.18 14.65 



Fe^Os 3.59 2.14 0.57 3.41 



FeO 8.25 8.24 9.07 6.96 



MnO 0.44 0.09 0.13 0.07 



MgO 7.63 7.97 8.39 7.95 



CaO 10.70 10.27 8.60 9.33 



Na,0 2.14 1.54 2.79 2.64 



K2O 0.39 1.06 1.26 0.75 



TiO^ 1.41 1.17 1.13 



P.O5 0.14 0.17 0.18 



H.O ( ) 1.33 1.70 3.04 



CO. ' ^-^^ ' 



0.63 

 '' ' ) 



Analysis I was recast by Hawes to show percentage of mineral con- 

 stituents as follows : 



Anorthite, 15.53; albite, 22.16; potash feldspar, 2.32; augite, 54.47; 

 titanic iron, 2.68; magnetite, 1.76; apatite, 0.32; total, 99.23. 



The augite was isolated by specific gravity solutions and found to have 

 the following composition : 



SiO, 50.71 



ALO3 3.55 



FeO 15.30 



MnO 0.81 



CaO 13.35! 



MgO 13.63 



Na„0 1 



K.O I 1-48 



Loss on ignition 1.17 



^» I. West Rock, New Haven. Conn.. G. W. Hawes, Analyst Proc. U. S. Nat. Mus., vol. 

 4, pp. 129-134, 1881. 



II. Watchung Mt, N. J., L. G. Eakins, Analyst. Bull. 150, U. S. Geol. Surv., p. 255, 

 1898. 



III. Scotch Plains, N. J., R. B. Gagk, Analyst, Ann. Rept. State Geol. of N. J. for 

 1907. 



IV. Nr. Springfield, N. J., R. B. Gage, Analyst, Ann. Rept. State Geol. of N. J. for 

 1907. 



