FENNER, THE WATCHUNG BASALT 159 



Slide 61 is plainly a shattered glass, with whose angular fragments 

 considerable quantities of reddish-brown clayey sediment from the under- 

 lying lake-bottom are mingled, forming a remarkable-looking mosaic. 

 The greater portion of the glass breccia is now altered to analcite and 

 chlorite, but in certain areas albite groups survive. Slide 119 is quite 

 similar in origin, but alteration has proceeded to the calcite period. In 

 many places, nevertheless, remnants of albite groups and a small quantity 

 of pleochroic green amphibole are perceptible. 



In 12, we have again a breccia mingled with sedimentary dust, but the 

 greater portion of the glass is now represented by groups of interlocking 

 albite crystals. The complex appearance is illustrated by Plate XII, 

 fig. 1. In this, the lighter areas throughout are mostly albite, through 

 which there is a sprinkling of insoluble residual dust (TiOg or MnOg), 

 distributed without regard to the crystallization of albite. The light 

 gray in the figure is chloritic material which appears to have migrated 

 into cracks, and the darker portions are chiefly foreign sediment. Diop- 

 side crystals are present in several places in the slide. The^r outlines 

 appear rounded, whereas the interiors have remained perfectly fresh. A 

 little acicular amphibole is visible. The effects of later alteration are 

 represented in a little calcite and in the bands of chlorite. In none of 

 the slides in which the reddish sediment is present does it seem to have 

 been affected in the slightest degree by the processes of alteration. 

 Although it appears that the solutions reached it at the early period at 

 which albite and amphibole were formed, nevertheless its areas and lines 

 of distribution remain sharp and distinct. 



In 120, a little albite and amphibole are scattered through zeolitic 

 material. In one portion of the section, there are indications of an orig- 

 inal glassy texture. In 59, the groups of minute quartz crystals shown 

 in Plate XI, fig. 4, occur in what was originally a glass breccia. In those 

 slides in which the geometrical figures similar to those illustrated in 

 Plate XI, fig. 5, and Plate XII, fig. 5, appear, the distribution of min- 

 erals is suggestive of replacement of a breccia. 



On the whole, the processes of recrystallization during this period are 

 believed to have acted so vigorously upon the glass that a very small por- 

 tion of that to which the solutions gained access escaped such thorough 

 transformation that the structure was almost completely destroyed. A 

 decided contrast is presented to the effects of the second period (that of 

 zeolitic alteration). In the latter, it is possible to trace with ease the 

 progress of the changes. In the less altered portions, the channels through 

 which the solutions percolated may be followed and the differential effects 

 upon more and less soluble material and the gradual spread of the areas 

 noted. 



