TYPES OF FOREIGN INCLUSION^ 9? 



of the magma loaded with the dissolved material drawn out into it. The 

 superheated water and dissolved salts acted as " mineralizers " in a gen- 

 eral way to produce the glass with spherulites, the plumose pyroxene, 

 the coarse pegmatitic or poikilitic plagioclase, the large skeletonized 

 magnetites, the micropegmatitic albite, and all the indications of rapid 

 and abnormal crystallization and resorption. A remarkable differentia- 

 tion has taken place in interstitial remnants of the magma into (1) a 

 dark, much hydrated, glass (palagonite), in which beautiful calcite spher- 

 ulites and sphserocrystals of ankerite and blue quartz have formed, and 

 (2) an acid quartz-albite ground, which surrounds the palagonite, and 

 has also been extravasated in small dikes, which I have called holyokeite. 



Detailed Descriptions 

 central explosion breccia 



The trap sheet is seen on the west to rest on a coarse buff sandstone 

 or conglomerate, and there is no indication that any material has been 

 carried up from below. It is thus not probable that this is a case com- 

 ing under the Meriden type. On the contrary, at the nearest outcrops 

 of the surface of the sheet areas of many acres are full of an indurated 

 mud of exactly the same texture and color as that found here in the 

 center of the sheet. It is therefore probable that the reservoir type is a 

 downward extension of the Titans Pier type. Furthermore, the frag- 

 ments of sandstone found in the breccia are sometimes perfectly stratified, 

 showing that they had been sufficiently indurated at the surface to be 

 transported into the mass without being wholly broken up, and this is 

 also the case with the mud inclosures at the surface. Further, this in- 

 cluded sandstone contains many scales of graphite, which is a widely 

 disseminated constituent in the Triassic sandstones, making it certain 

 that they have a common derivation. Moreover, the abundant fractur- 

 ing and the cementation are confined to the central band, where the 

 Assuring is an original structure, and not one due to the upturning of 

 the rocks, since large blocks of the trap were broken open in the blasting 

 and isolated fissures found within them. 



The paragenesis of the pearl-gray vein fillings of these fissures is ex- 

 ceedingly interesting for our purpose. On either wall of every fissure 

 is a layer of a ferruginous carbonate, probably an ankerite.* Within 

 these rusty carbonate layers are quartz layers, generally granular, but 

 sometimes in perfect limpid crystals, one-third of an inch across, which 



*This is, under the microscope, often made up of perfect rhombohedra with convex faces, 

 which are limonite-dusted in concentric bands. In basal and vertical sections of each rhom- 

 bohedron there appears a perfect large black cross. The curved-face form is in effect a com- 

 posite with many radiating axes. This produces the same result as a radiate-fibrous structure. 



