1894. | NEW YORK ACADEMY OF SCIENCES. 189 
mostly wanting. The orthoclase of the phenocrysts appears to 
be older than the plagioclase, that in the ground mass younger. 
Hornblende, when original, occurs either in well-defined crys- 
tals or irregular masses of deep green color and strong pleo- 
chroism. It is sometimes very difficult to get it thin enough to 
be translucent. The secondary hornblende is uralitic, with light 
green and yellow pleochroism, and is found paramorphic after 
biotite and also after the dark-green hornblende, instances of 
the progressive alteration of either being not infrequently seen. 
Piotite is mostly in well bounded crystals, and is almost as 
abundant as the hornblende in unaltered material, but tends 
Fic. 1, QUARTZ-DIORITE. 
Enlarged 5 diam. Spec. 113 Q=quartz; P—plagioclase ; 
O=orthoclase ; H—hornblende; B=biotite. 
strongly to alter to secondary hornblende interleaved with 
epidote. 
Apatite is unusually abundant for this kind of rock, and 
forms a good characteristic whereby to make sure of the identity 
of any part of the intrusion. It isin the usual small crystals and 
mostly included in or associated with the ferromagnesian 
silicates. 
Zircon is likewise quite abundant, especially in connection 
with abundance of orthoclase. It occurs in remarkably well 
