ROCKS FROM NORTHERN AND CENTRAL CHINA. 427 
stresses. Subsequent crystals of biotite and tourmaline have begunto 
grow across the schistose structure, but they are few and small. 
Scapoiite-staurolite schist, No. 158.—Our specimen of this schist was 
taken froma pebble in conglomerate (106 and 107) south of Fang-lan-chén, 
Shan-si. The conglomerate is believed to be of later Algonkian age (Hu-t’o), 
but the schist pebbles have their closest relatives among the intensely 
metamorphosed sediments of the Wu-t’ai series; and it is appropriate, 
therefore, to describe the rock as a member of that series. The schist 
resembles most closely certain members of the Shi-tsui section. 
A very fine-grained schist which cleaves with facility only along cer- 
tain planes sheeted with biotite flakes. Under the microscope. the body 
of the rock shows a thoroughly schistose structure; it is almost iden- 
tical with that already described for No. 86. The schist is interrupted 
by porphyritic crystals of several minerals characteristic of the deep zone. 
Large flakes of biotite are interleaved with secondary quartz in the coarser 
laminz of the rock. Ragged yellow staurolites are associated with them. 
Throughout the rock little prisms of tourmaline lie at all angles regardless 
of previous structures. 
Scapolite* occurs in elliptical bodies distributed sparsely throughout 
the rock. The lenses have no definite boundaries, but are intimately asso- 
ciated with the biotitic ground-mass, while inclusions of magnetite, quartz, 
and tourmaline are so abundant as to obscure the scapolite itself in large 
measure. The age of the scapolite is somewhat doubtful. The elliptical 
form of the sections and the bulging of the schistose layers around them 
suggest original grains deformed under mass-mechanical conditions. On 
the other hand, the inclusions in the scapolite are part of the schistose 
matrix and lie in parallel lines. Among them are tourmaline and biotite— 
both anamorphic products. It seems more probable, therefore, that the 
scapolite is one of the latest minerals in the rock; that it grew 7m situ and 
occluded during the process the crystals it now contains. 
This schist represents intense metamorphism of a pelite. Van Hise 
regards staurolite and tourmaline as typical minerals of rocks which have 
suffered the extremity of alteration in the zone of anamorphism. ‘The 
fact that recognizable quartzites are associated with this schist in the 
Wu-t’ai series only adds to the weight of evidence that quartzite is won- 
derfully resistant to metamorphism. 
Scapolite-biotite schist, No.87.—This is only a peculiar phase of the schist 
last described. It is associated with garnet schist (Plate XVIII, stratum 7). 
The rock is very similar to No. 86, except that the black biotitic disks 
are absent, and in their place we see many grayish spots of ovoid form— 

* Although this mineralresembles orthoclase superficially, in this case it was identified by the uniaxial 
interference-figure and high birefringence. 
