


1891] Mineralogy and Petrography. = fis 
Dr. Wolff” calls attention to the existence of ottrelite and ilmenite 
schists among the Paleozoic crystalline rocks of the Taconic region in 
the Green Mountains and in Massachusetts and Rhode Island. The 
Rhode Island rocks comprise micaceous schists and graywackes. In 
the former are grains of quartz, scales of muscovite, and occasional small 
patches of chlorite and bands of a mixture of graphite and ilmenite. 
Ottrelite crystals are scattered indiscriminately among the other con- 
stituents. In the graywacke the ottrelite occurs in irregular plates, 
ewhich are fiee from optical deformities, while the other components of 
the rock give evidence of having been subjected to intense pressure. 
Even the mica, which owes its presence to metamorphic agencies, is 
bent and twisted. The absence of optical deformities in the ottrelite 
points to a very late origin for this mineral. The author ae briefly 
describes a graphite-schist with ilmenite plates from R Island. 
All the Rhode Island rocks are known only in boulders, Singaeliaf 

‘describes specimens of glassy lava from Vesuvius in the cabinet of the 
University of Berlin. Those from the streams of 1753 and 1809 con- 
sist largely of glass in which are tiny perfectly formed crystals of leu- 
cite and olivine and good crystals of augite and plagioclase. Other 
leucites are skeleton crystals, with their edges sharply defined, but their 
faces hollow. Two other specimens contain glassy portions between 
crystalline portions. Of these, one from the flow of 1822 contains 
ornblende, and another, whose age is unknown, has its anorthite and 
other crystals surrounded by rims of little rutile needles. ——The 
ophiolites of Essex Co., N. Y., and the serpentines from Aque- 
duct Shaft No. 26, New York city, and from near Easton, Pa., have 
resulted by metasomatic changes from pyroxene, according to Merrill.® 
In the first-named rock the larger part of the serpentine, which is light 
green in color, is from a colorless pyroxene. Small particles of a 
darker-colored serpentine are scattered through the rock, and in these 
are enclosed graphite scales. Thin sections of these portions show 
them to consist of calcite, dolomite and serpentine. Originally they 
were probably composed of the first two minerals only. The serpen- 
tine is a subsequent formation, but by what method it was produced 
the author has not succeeded in determining. A remarkable example 
of a Huronian volcanic tufa, from the nickel region at Sudbury, Can- 
ada, is reported by G. H. Williams as composed of a glass breccia 

7 Bull. Mus. Comp. Zool., XVI., No. 8, p. 159. 
8 Neues Jahrb. f. Min., etc., B.B. VIL, p. 417. 
€ Proc. U. S. Nat. Mus., XIL, p.595 ; Washington, 1890. 
10 Bull. Geol. Soc. Amer., Vol. IL., p. 138. 


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