98 B. K. EMERSON — PLUMOSE DIABASE AND PALAGONITE 



are at times amethystine. A third layer is a calcite in scalenohedra, J? 3 , 

 sometimes terminated by — h R, or in cleavable masses coating the other 

 crystals or rilling the cavity, with here and there a rich oil-green lustrous 

 grain of apatite completing the filling. These veins are thought to have 

 been formed immediately after solidification. It is interesting that there 

 is no trace of datolite or zeolites in these veins, as both are abundant a 

 few miles south and generally in the trap. They seem to occur only 

 where large faults go through the trap dikes. In the north part of the 

 reservoir area larger fragments of a gray flat-bedded calcareous sand- 

 stone occur, included in the shattered trap, with many mica scales on 

 the laminae and many scales of graphite imbedded. These sandstone 

 fragments are quite large, and, in contrast to the small and rare fragments 

 of the marly sandstone in the breccia farther south, they contain, indi- 

 cating the violence of the explosions, small fragments about an inch 

 across of the same coarse weathered gabbroid diabase. These occur just 

 south of the sharp bend in the road between Hitchcock pond and Rock 

 valley. The rock of the breccia varies in coarseness rapidly. The stout 

 plagioclase blades are often 8 to 10 millimeters long and are opaque 

 white because they are uniformly changed to mats of coarse tufts of a 

 white mica like the plumose muscovite of granite. This I take to be an 

 original structure, produced by the continued activity of the heated 

 waters and not a late product of subaerial influence, since it is uniform 

 in the center of great blocks newly blasted out. It is metamorphism 

 and not weathering. The ferromagnesian constituent is often changed 

 to a deep green chlorite. The immediate influence of the abundant 

 water is thus very strong, and is different from what it is in the schlieren 

 rocks. All the minute mud fragments are surrounded by a broad band 

 of crystalline quartz and calcite, showing that they have all shrunk and 

 given up much water to the trap. 



OCCURRENCE OF ANALCITE 



In the small steam holes in a block of altered gabbro, near the center 

 containing holyokeite dikes, the cavities are filled with a colorless non- 

 polarizing mineral with cubical cleavage, whose index of refraction is 

 below the balsam. This is doubtless analcite. 



GENERAL DESCRIPTION OF THE SCHLIEREN 



The schlieren appear in irregular bands or sheets from a fraction of 

 an inch to several feet in the smallest dimension and tapering off to a 

 thin edge in the midst of the fine-grained trap. Where these bands 

 come in contact with the fine-grained trap the transition was not marked 

 by a fissure as if one while hot had been injected in the other after its 



