J. F. Kemp — Basic Dike near Hamburg, N. J. 301 



it is the same as the mica of the theralites, with which rocks 

 Professor Rosenbusch regards this dike as related. 



Fig. 2. 



Fig. 2. Micro-drawing of normal dike rock. Actual field 3-5 mm in diameter. 

 B. biotite, P, pyroxene, A, analcite. The general shading is uniform for each. 



The pyroxene is faint yellow in color and affords extinctions 

 up to 33° as measured. It is apparently identical with the one 

 mentioned in the writer's paper on the elasolite-syenite, as oc- 

 curring in an elasolite-porphyry (see paper on the Beemerville 

 syenite, p. 66.) The basal sections show the emergence of an 

 optic axis not much inclined to them. The plagioclase is in 

 small rods but is not abundant. The analcite is almost or quite 

 isotropic. It gelatinizes readily and stains a deep tint. Cracks 

 showing the cubical cleavages are often to be seen. If the 

 analcite is secondary after original nepheline, this mineral must 

 have been very abundant. As all the other components of the 

 rock are perfectly fresh, it would indicate that the nepheline 

 has fallen an easy prey to atmospheric agencies. 



The spheroidal inclusions offer the point of chief interest. 

 This is heightened because they have been thought to indicate 

 leucite. In the fall of 1890, Mr. O. A. Derby, of Brazil, spent 

 several days with the writer, and on looking over the material 

 from this dike, was at once impressed with its resemblance to 

 certain Brazilian dikes, in which similar spheroidal masses oc- 

 cur, which he has regarded as alteration products after leucite. 

 At his request a specimen was given him and on this are based, 

 the remarks upon the rock, which appeared in the JSfeues Jahr- 

 buch, 1892, ii, p. 153, from Dr. E. Hussak. Dr. Hussak refers to 

 the earlier paper on the " Porphyrite Bosses" already cited, but 

 it should be noted that the materials, on which that contribution 



