ROCKS FROM NORTHERN AND CENTRAL CHINA. 401 
speckled appearance. The chloritic hornfels with which it is in contact 
is a dense, dark, green-gray rock which shows no trace of its original 
structure. It is pierced by numerous radiating tubular bodies of quartz, 
with zoisite, which radiate outward from the contact. 
The mass of the rock consists of medium-sized and fairly idiomorphic 
alkali feldspars, with hornblende, augite, and various accessory and second- 
ary minerals, such as quartz, ilmenite, sphene (and leucoxene), apatite, 
zircon, actinolite, epidote, zoisite, chlorite, and tourmaline. 
The feldspars are largely albite, but there are also many scattered 
bodies of orthoclase. In general the feldspars are quite fresh, and exhibit 
no features which can be referred to as surely of a secondary nature. Gran- 
ules of zoisite are, however, scattered abundantly throughout the rock, 
and it may be that they are alteration products derived from more calcic 
feldspars which have been completely changed into alkali feldspars and 
zoisite, as suggested in the case of No. 137. The facts observed do not 
permit us to decide upon this question. 
Of the common ferro-magnesian minerals, both augite and hornblende 
are present. Sometimes the amphibole incloses the pyroxene, but usually 
the two minerals occur in separate bodies. The pyroxene is colorless 
except for the cloudy brown products of alteration by which most of it is 
obscured. From the edges of the crystals needles of a pale amphibole 
(actinolite?) have grown outward as a fringe, while secondary chlorite has 
invaded the crystals irregularly. It is, therefore, much decayed. 
The original hornblende was brownish, as is indicated by certain 
brown patches which still remain. This has been extensively changed to a 
green color, and even the green has in a large measure been bleached out, 
so that many of the crystals now appear as pale-greenish amphibole pos- 
sessing only the faintest pleochroism.* Alterations of the hornblende, 
like those of the pyroxene, result in the formation of chlorite and a fibrous 
amphibole of pale emerald-green color. The abundant grains and small 
crystals of zoisite, with more or less of epidote, which are so closely asso- 
ciated with these greenish minerals, may have been derived in part from 
the alteration of primary amphiboles and pyroxenes. 
Some of the larger crystals of zoisite inclose yellowish epidote. Apatite 
forms rather large prisms, and zircon is quite rare. Although the tita- 
nium minerals are not abundant, ilmenite with secondary leucoxene and 
sphene are present in considerable quantity. 
Contact phenomena.—The syenite is in sharp contact with a hornfels 
which represents the green slates of the Sin-t’an formation.t This horn- 
* References to these changes in hornblendes have already been made in connection with No. 137. 
+ For a slightly metamorphosed phase of these slates, see No. 141, 
