LITHOLOGY. Ist 
light their color is brownish red. The feldspar shows its characteristic 
bandings in polarized light, but is usually troubled and clouded by de- 
composition. The bandings are sometimes almost obliterated on account 
of alteration, and then the crystals do not become dark in any position 
between crossed Nicols, but show only the effects of an aggregate of 
secondary products. Crystals or grains resembling magnetite are found 
intact; but often a black rounded kernel or skeleton is found in a gray- 
ish mass, which is recognized as characteristic of the decomposition of 
titanic iron. Very minute needles of apatite, which pierce through the 
other minerals, and which are often grouped together in large numbers, 
are invariably present. Other products have also resulted from decom- 
position, a characteristic one of which is epidote. This is often macro- 
scopically seen filling amygdaloidal cavities, but is more often seen with 
the microscope, especially in sections that show a much altered feldspar. 
It appears as a very light yellow, slightly dichroic product, often in very 
minute particles which in polarized light assume the most brilliant colors, 
Calcite is rarely absent. It fills the cavities and pores, and, when not 
visible with the microscope, a specimen of the rock when moistened with 
acid will effervesce, and indicate its pressure. Biotite is not rare, but 
whether as an original or a secondary product is not certain. Quartz is 
not uncommon, but it is plainly a secondary product. These are the 
most general characteristics of the first well marked variety, which may 
be called the chloritic type. 
There are some large dykes of this rock on the road from the Glen 
house to the summit of Mt. Washington. In sections of specimens the 
double system of twinning, which so often characterizes labradorite, is 
conspicuous. A section of a specimen from Stark indicates that the augite 
is almost entirely gone, and chlorite takes its place, fills cavities in the 
rock, and forms little concretions in spots. A rock near the Sagamore 
house resembles the last, but in it much more epidote has been formed 
and less chlorite, and, as is usual in such cases, the feldspar has suffered 
more and the augite less. This rock also contains pyrites. A rock 
that forms a dyke which cuts the gabbro on Mt. Washington river is 
remarkable for its large content of pyrite and magnetite. The augite is 
in small grains, and has been altered in part into chlorite, and in part 
into hornblende. The decomposition of a light-colored diabase has 
