488 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 57. 



in the ores, and is more glassy at the borders than in the center. The 

 ores are not noticeably metamorphosed. 



In its freshest condition tlie rociv of this dilve is dark greenish-gray and fine 

 grained, tlie only minerals recognizable to the unaided eye being small prisms 

 of hornblende, specks of pyrite, and scattered grains or granular inclusions of 

 quartz up to an inch in diameter. The microscope shows a holocrystalline ag- 

 gregate of abundant phenocrysts of hornblende in a groundmass of the same 

 mineral, with a calcic-plagioclase in minute laths. Larger phenocrysts, pos- 

 sibly augite, have been completely altered to calcite, serpentine, and secondary 

 amphibole. The rock appears originally to have had some glass in the ground- 

 mass, but it is now altered to chlorite. The quartz inclusions are much cor- 

 roded and embayed and are usually surrounded by reaction rims in which 

 spherulitic quartz appears in the groundmass. The rock is probably an odinite, 

 hornblende being too abundant for kersantite, in which biotite is the princi- 

 pal dark mineral. The quartz grains are presumably not original but are In- 

 clusions derived from the quartzose sediments through which the dike was 

 intruded. 



No other rocks of this character have been seen from this mine. 

 This suggests that the Hecla dike may not be as simple as is generally 

 supposed and lamprophyric magmas of two types may have been 

 injected into the fissure at slightly different periods. 



Hornblende-quartz roch., Bailey''s Pond. — At the side of the old 

 road, at Bailey's Pond, south of the river, a short distance east of 

 Kellogg, there are several lamprophyric dil?es. Four or five narrow 

 black dikes averaging each about 2 feet in thickness outcrop almost 

 horizontally, one above another, along the face of the cliff. These 

 are almost aphanitic in texture and are very much altered but appear 

 to have originally been spessartites. In weathering they character- 

 istically give rounded cobbles resembling water worn bowlders. The 

 uppermost dike appears originally to have been somewhat larger 

 than the others but here there are clearly two dikes intruded into 

 the same fissure. Tlie dark mafic rock is in places shattered, forming 

 a breccia cemented by the later much more feldspathic rock. In 

 other places the later intrusion has followed the bottom contact or 

 the top contact or sometimes both giving a central layer of the dark 

 rock sandwiched between two layers of the more feldspathic rock 

 the contact in all places being clean-cut with no mingling of the two 

 materials. The dark rock of this dike in the hand specimen looks 

 fresher and more completely crystalline than that of the dikes below. 

 It is a fine-grained equigranular rock of dark greenish-gray color, 

 which to the unaided eye shows numerous glittering prisms of black 

 hornblende. Megascopically it is indistinguishable from the typical 

 fresh spessartites of the Standard and other dikes. 



Under the microscope this rock is seen to consist almost entirely of 

 hornblende and quartz, feldspar being entirely absent. Biotite forms 

 ragged and much resorbed phenocrysts now almost entirely altered 

 to chlorite. The biotite differs from the ordinary biotite of the 



