ORIGIN OF FOLIATED CRYSTALLINE ROCKS 307 
OTHER SERICITE SCHISTS WHICH HAVE PROBABLY ORIGINATED 
FROM QUARTZITE 
It is interesting, at this point, to recall the case of the sericite 
schist described by Thiirach" as containing abundant zircons. This 
rock is associated with the Taunus quartzite which also contains 
a large content of zircon. While the shale-like composition of the 
sericite schist may in large part be due to the original argillaceous 
character of the rock, it is possible that, to some degree at least, 
it results from a more silicious rock by a loss of quartz and a 
concentration of impurities. 
More striking is a case described by Derby? in which there 
seems good reason for supposing that the sericite schist has a 
similar origin to that at Waterloo. Derby states that in appear- 
ance this rock is ‘‘a purely micaceous rock with no evidence, even in 
the heavy residue, of more than the merest trace of free quartz and 
hematite... . . : The rock probably contains over 80 per cent of 
an iron bearing sericite with, perhaps, 7 per cent, more or less, of 
chlorite and a small percentage of quartz and earthy iron oxide. | 
Washings reveal a small amount of secondary tourmaline, of which 
the grains appear to be secondarily enlarged, and worn zircons of a 
size and abundance that seem extraordinary in a rock of such fine grain 
and of so purely argillaceous character.’ The analysis of this 
sericite schist is given below in column 1. 
at 2 
S1 Oy rice. Vceeecrp tame ae 47.83 8.85 
TANIA OR Situs ai ty ee a chee note 20.75 26.22 
GS Ogre ni cieten es apres: « 8.51 3.01 
THEO) PRE te nae \ Uscuiieral: Mel! Sc fees ia a7 
IY [fe eee Smear cuca 2.43 .63 
KO etre west tees ete IO.42 8.44 
Nias OF einccoce eter | een Naksenaees Baits) 
ETE Ogre roma ee yare eral|| Chee cio he PGR 
IKON odopenwon oes 5-33 Rice preg 
1. Schist found loose in the diamond mine of Sao Jodo da 
Chapada, but presumed to come from a schistose layer in a con- 
glomeratic quartzite. 
t Wiirzburg, Phys.-Medic. Gesellsch., XVIII (1884). 
20. A. Derby, Am. Jour. Sci., 4th Ser., X (1900), 207-16. 
