100 THE CRYSTAL FALLS IKON-BEARING DISTRICT. 



though iu most cases tliey are rei)laced by sphene. In some cases the 

 alteration product is not well enough individualized for one to diagnose it 

 as sphene, and it should perhaps be called leucoxene. In some of the fine- 

 grained rocks the material in the angles between the feldspars consists pre- 

 'dominately of grains of magnetite. This abundant magnetite renders the 

 rock very dark, giving the rare purplish-black lavas. 



The most of the hornblende has a light-green color. A lesser portion 

 shows a decided bluish tinge, and gives fairly strong pleochroism. This 

 resembles the hornblende, which in the coarse dolerites is undoubtedly sec- 

 ondary after the augite and it is considered to be secondary after the origi- 

 nal augite iu these rocks. 



The original augite was presumably in most cases present in wedge- 

 shaped pieces filling the spaces between the feldspars, and consequently the 

 hornblende pseudomorphs never show augite outlines. No imaltered augite 

 was observed amongst the hornblende fibers. The fine fibers frequently 

 form a fringe beyond the original boundaries of the pieces and penetrate 

 the adjacent feldspar. Quite frequently the secondary hornblende shows 

 partial alteration to chlorite and epidote. 



Though careful search was made for olivine or indications of its pres- 

 ence, no traces of it were found, and I have concluded that these basic vol- 

 canics were essentially nonolivine bearing, though it would be rash to state 

 that such rocks did not contain some olivine. 



The calcite is usually found in irregular secondary granular aggregates 

 scattered tlu'ough the rock, and evidently replaces the other minerals. Less 

 commonly it is seen as an infiltration product along fissures. 



A second form of the occurrence of calcite in the nonporphyritic meta- 

 basalts, and one not so common as the granular aggregate, is that of large 

 porphyritic automorphic rhombohedra and scalenohedra Avhich lie embedded 

 in the eruptive grouiidmass. Such a rock, as, for instance, Sp. 32472, shows 

 macroscopically large rhombohedral phenocrysts in a green groundmass. 

 On the weathered surface are ferruginous rhombohedral cavities, once occu 

 pied by the carbonates. The groundmass consists of rather fresh plagioclase 

 microlites, between which are observed some quartz, fresh magnetite crys- 

 tals, and lastly chlorite flakes as alteration products of originally present 

 bisilicates or glass, or both. The texture is undoubtedly that of an eruptive. 

 The carbonate is more or less ferruginous, brown iron hydroxide resulting 



