1883.] 489 [Wadswortn. 



ish, and reddish brown appearance. It remains only in remnants 

 surrounded by the secondary hornblende. The cleavage is usu- 

 ally well marked although in one or two cases it is suggestive of 

 the augitic variety. The hornblende is principally in needle-like 

 fibers making up larger masses which optically have the same ori- 

 entation. It is strongly pleochroic varying trom a yellowish green 

 to grass green and bluish green. The hornblende fibres extend 

 out from the diallage through the adjacent feldspar and quartz in 

 bundles and rods. The feldspar is chiefly triclinic, and is greatly 

 altered, containing much epidote, chlorite, quartz, etc. The 

 biotite shows dichroism from yellow to dark brown, occurs in 

 masses and plates, not abundant, and generally is associated with 

 the hornblende. The titaniferous iron is mainly altered to " leu- 

 coxene." The epidote is in nearly colorless granules scattered 

 throughout the section, and in larger pale yellow masses, showing 

 cleavage and twin structure. The quartz is in irregular masses in 

 the feldspar and in the interspaces between the other minerals. It 

 contains fluid cavities with moving bubbles and numerous gran- 

 ules, and needles ot epidote, hornblende, etc. The apatite occurs 

 in the usual elongated crystals, and is especially abundant in the 

 chlorite. This mineral is in fibres and scales forming masses 

 which sometimes show a dichroism varying from yellow to green, 

 but at others are not dichroic. Some secondary feldspar was 

 observed. 



This rock I regard as once having possessed the characters of a 

 gabbro or coarsely crystalline basalt (dole rite or diabase), but 

 that it has since been subject to great alteration. So far as made 

 out the feldspar, diallage (or augite), and titaniferous iron were 

 the original minerals of the rock — if any olivine existed it has - 

 entirely disappeared — and that through their alteration by perco- 

 lating waters (thermal?) has been produced the hornblende, chlo- 

 rite, biotite, quartz, epidote, " leucoxene," the ferruginous prod- 

 ucts, and probably the apatite, etc. 



In its present condition most lithologists would call this rock a 

 quartz diorite, but I would prefer to class it under the species 

 from which it appears to have been derived by alteration, that is 

 under the basalts as a gabbro or diabase. This I would prefer in 

 order to show its natural relations, since the term diorite now in- 

 cludes a great number of rocks produced by the alteration of 

 different species running from basalt to granite. 



