WARREN. — ALKALI-GRANITES AND PORPHYRIES. 217 



about the ends where it is usually seen in greatest abundance. Al- 

 though the marginal aegirite may form a continuous mass about the 

 hornblende, it more often consists of a number or many individual 

 crystals which may be parallel, slightly divergent, or subradiate in 

 arrangement, and these project out into the feldspar or quartz most 

 irregularly and are often accompanied by numerous semi- or wholly 

 detached particles. It is also not at all uncommon to find inclusions 

 of aegirite lying unorientated in the hornljlende. While these latter 

 favor the margins they often lie well within the hornblende substance. 

 Many of the original hornblende grains have evidently been broken 

 apart before crystallization had ceased in the magma, for the separated 

 parts of what was once obviously a continuous crystal may be seen 

 with its broken ends margined with aegirite exactly in the same man- 

 ner as the natural ends. It is not unusual to find a hornblende grain 

 accompanied by a development of hornblende prisms, sometimes 

 with a divergent arrangement, which project out unto the adjoining 

 minerals : again the hornblende area may consist of a mass of prismoid 

 crystals more or less grouped and of various orientations accompanied 

 by other materials — grains of iron oxide (chiefly magnetite) titanite, 

 calcite, granular feldspar and even fluorite. Such groups appear to 

 be in large part at least recrystallizations. In such cases the aegirite 

 originally present seems to have suffered little or no change. This 

 hornblende is always of the deep blue type (riebeckitic). The min- 

 erals mentioned as accompanying the secondary hornblende can be 

 seen to follow in the arrangement of their grains, to some extent at 

 least, the structure of the original mineral. Perhaps the titanite is 

 the only one of these calling for any special notice. Where present its 

 amount may vary from very little to an amount that, in extreme cases, 

 may constitute perhaps one fifth of the whole area. It consists of 

 grains or aggregates of grains whose outward form seems determined 

 by the structure of the original hornblende, or of those minerals which 

 developed simultaneously with it. It thus lacks entirely the habit 

 usually associated with titanite. Its optical properties serve, how- 

 ever, to prove its identity. It seems to be secondary and doubtless 

 derived its titanium from the titantium content of the original 

 hornblende, or in cases where the amount of titanite appears to have 

 been much too large for the amount of titanium present in the horn- 

 blende (probably not in excess of 1.5%; see anal, of hornblende from 

 pegmatite — Warren and Palache, loc. cit., p. 124), from included 

 aenigmatite or ilmenite. The lime cannot have come from the horn- 

 blende and the presence of calcite with the titanite is suggestive that 



