320 



WATSON AND CLINK 



IGNEOUS DIKES IN VIRGINIA 



colored areas (phenocrvsts) in the rock are occupied by calcite, fibrous 

 zeolites, and an isotropic mineral identified as analcite. Analcite usually 

 occupies the outer part of the area and calcite the center, the latter 

 always being in excess. Analcite also occurs as a constituent of the 

 ground-mass and is the original mineral from which the calcite and 

 fibrous zeolites of the light-colored areas (phenocrvsts) have been derived. 

 These relations are well shown in figure 2. 



Chemical composition and classification in the quantitative system. — 

 For the purpose of studying the chemical composition of this rock, the 

 Glick Farm dike was selected as the freshest and most representative. 

 In the table below is given the analysis of this rock by Mr. J. Wilbur 

 Watson, and analyses of related rocks are added for comparison. As 

 will be observed from the analysis (column I), the Virginia rock was 

 not fresh, although it had the appearance of such in the hand specimen. 

 Partial alteration of the rock is also shown in the microscopic study of 

 thin-sections. One of the most abundant secondary minerals in the rock 

 is calcite, as shown under the microscope and by the large percentage of 

 C0 2 in the analysis. 



Analyses of Teschenite ( A)ialcite-l)asalt) and related Rocks 



Si0 2 40.40 



A1 2 3 13.49 



Fe 2 3 



FeO 



MgO 



CaO 



Na 2 



K 2 



H 2 0- 



H 2 0+ 



Ti0 2 



P 2 5 



MnO 



BaO 



C0 2 



S 



I 



II 



III 



IV 



V 



VI 



40.40 



46.77 



39.64 



41.10 



48.35 



47.82 



13.49 



14.91 



16.98 



14.82 



13.27 



13.56 



5.87 



7.80 



6.61 



2.35 



4.38 



4.73 



4.88 



4.90 



9.31 



10.38 



3.23 



4.54 



8.01 



2.94 



6.65 



9.43 



8.36 



7.49 



10.02 



6.30 



10.58 



10.56 



9.94 



8.91 



3.45 



4.97 



5.95 



3.94 



3.35 



4.37 



2.94 



2.37 



3.09 



1.28 



3.01 



3.23 



0.61 

 3.06 



0.92 1 



4.28 ) 



1.32 



f 0.39 

 1 2.31 



0.90 1 



2.89/ 



3.37 



2.21 



2.31 





3.20 



0.52 



0.67 



1.09 



0.98 





0.19 



0.40 



1.10 



0.63 



0.29 





0.14 



0.19 



Trace 





0.04 





0.06 



0.54 



0.16 



3.72 



Trace 





0.26 



0.30 





0.19 











Trace 









Rest 



0.34 



0.25 



100.5' 



99.90 100.13 100.41 100.01 100.20 



I. Teschenite (analcite-basalt) from dike on Glick farm, 4 miles east of 

 Mount Solon. Augusta County. Virginia. J. Wilbur Watson, analyst. 



II. Teschenite from Mapleton township. Aroostook County. Maine. W. F. 

 Hillebrand. analyst. (Described by H. E. Gregory in Bulletin 165, U. S. Geo- 

 logical Survey, 1900, p. 183.) 



