Pirsson and Washington — Geology of New Hampshire. 503 



stout tabular form l-3 mm long, of a pink color and with 

 slender needles of hornblende also about l-3 mm long, these 

 two with distinct fluidal arrangement! GTroundmass compact 

 and of a medium, somewhat brownish-gray. 



Microscopic. — The study of the section shows that the rock 

 is much altered. The ground mass consists of small feld- 

 spar granules tending to a short lath-shaped form, and although 

 considerably changed it can be seen that both alkalic and 

 plagioclase feldspars are present. At first glance the impres- 

 sion is that of a rock of syenitic aspect, that the rock is an 

 altered monzonose, a gauteite in current phraseology ; but 

 further inspection reveals the fact that it is everywhere filled 

 with minute pseudomorphs of chlorite which, on grounds to be 

 presently mentioned, are thought to be pseudomorphs of 

 needles and microlites of hornblende. Were these latter pres- 

 ent, as they must have been originally, the rock would have a 

 distinct lamprophyric aspect and micro-hampshiroid habit. 

 This groundmass is dotted thickly with granules of calcite, 

 titanite and occasional ore grains. Scattered in it are infre- 

 quent phenocrysts of feldspar, which in spite of being more 

 or less filled with sericite shreds, show by the albite twinning 

 and extinction angles that they are of plagioclase. 



The most interesting and important features of the rock are 

 the hornblende phenocrysts and the process of alteration 

 which they have suffered, one hitherto unmatched in our 

 experience. The unchanged mineral is a brown basaltic one, 

 with strong pleochroism in yellow tones and similar to that 

 already described in the gilfordal camptonose (essexite) and 

 in the dikes : c and f>, dark yellowish brown ; a, ve^ pale 

 brown almost colorless, a pleochroism like many biotites. 

 Absorption strong, c = b > a. Angle of c on c about 9°. 

 Cleavage very good. These are the properties of basaltic 

 hornblende. What remains of the small microlites in the 

 groundmass shows that they are similar. 



These hornblendes are all more or less altered into pseudo- 

 morphs consisting of a pale green fibrous, almost isotropic 

 chlorite, grains of calcite and of titanite. The chlorite and 

 calcite as alteration products of hornblende present nothing 

 unusual, but, so far as we know, titanite as a secondary mineral 

 in this connection has not been described, and at first thought 

 it seems so unlikely an origin for it that the matter deserves 

 some consideration. 



Titanite secondary from hornblende. 



The titanite occurs in irregular grains and masses showing 

 no good crystal form, intermingled with the chlorite and cal- 

 cite in the pseudomorphs. Often it can be seen running into 

 the still unaltered hornblende in strips and wedges and 



