146 THE CRYSTAL FALLS IROy-BEAElNG DISTRICT. 



svutliotic twinning', showing the presence of plagioclastic feldspar, were 

 seen in places on the edge of the section. In the chlorite and quartz occur 

 large grains of fresh titaniferous iron ore, altering on edge to sphene, and, 

 most striking of all, large porphyritic, beautifully automorphic calcite rhombs 

 and muscovite plates in isolated individuals as well as in heaps of crystals. 

 The carbonate, which predominates, effervesces readily with cold HCl, but 

 is evidently ferruginous as it is yellowish when altered, and from it results 

 some of the ochre which colors the \'\^eathered surface of the rock. In other 

 sections the calcite phenocrj^sts are scalenohedra, with ^-ery few rhombo- 

 hedra. The terminal faces are not sharply defined. The sections resulting 

 from the scalenohedra are long, lath-shaped, and liaA'e pointed or irregular 

 ends, parallel extinction, and oblique cleavage. 



In passing from the centers toward the edges of the fragments, ^\e note 

 a marked diminution in the amount of carbonate, muscovite, chlorite, and 

 iron oxide, causing a consequent lightening in color of the periphery. This 

 gives the zonal structure noticeable upon the macroscopical examination of 

 the thin section. The schistose character of the fragments is caused bv the 

 parallelism of the chlorite flakes. 



The cement between the fragments is composed of quartz in rather 

 coarse grains, chlorite in larger flakes than in the fragments, and carbonate 

 in large porphyritic crystals, and also in minute rhombs included in the 

 quartz grains. Another phase contains considerable secondary plagioclastic 

 feldspar associated with the quartz in the coarser-grained portion of the 

 cement. As in some of the conglomerates and tuffs, the fragments are 

 observed lying in juxtaposition, the only cement between them being the 

 secondar}^ interpenetrating minerals. In some cases the edges of the frag- 

 ments have been so welded that one may pass from one pebble to the 

 adjoining one across an intervening lighter zone without detecting the 

 transition, unless changes in the amount of chlorite, iron oxide, and carbonate 

 are noticed. 



Nothing thus far mentioned would indicate the igneous origin of the 

 fragments, but that is indisputably proven by the amygdaloidal texture of 

 the specimens, than which I have seen none better, even in the freshest 

 volcanics. The outline of the cavities is marked b}' an accumulation of 

 grains of iron oxide, and the cavities themselves are filled by fine-grained 

 quartz having a small amount of chlorite associated with it. (Figs. A and B, 



