1891. | DERBY——-ON ACCESSORIES OF ROCKS. 205 
Pascoag, R. I. In the granite-of Vulcan, Menominee Co., Mich., they 
are discolored as if by superficial alteration. 
Monasite, giving the absorption band of didymiun, occurs in the 
granite of Westerly, R. I., Narragansett Pier, R. I., and the gneiss 
of Wessford and Ayer, Mass., Randolph, and East Pond, Waxefield, 
N. H. Inthe gneiss of East Blue Hill, Me., are grains that might be 
referred, from a microscopic examination alone, to monazite, but that 
fail to give the spectroscopic test, possibly from a_ deficiency of 
didymium. It is particularly abundant and characteristic in the 
Westerly granite and Randolph gneiss. In the latter the aspect of the 
mineral is precisely that of the Brazilian localities, while in the former 
its color and appearance is quite different from any yet seen elsewhere. 
The strong absorption band, high specific gravity and phosphoric acid 
reaction serve to identify it as monazite. 
Xenotime appears in minute octahedral crystals identical in aspect 
with those of the Brazilian rocks, in the gneiss of Wessford, Mass. 
The muscovite granite of Narragansett Pier and the pegmatite of 
Auburn, Me., which looked favorable for this mineral, failed to show 
it, possibly from insufficiency of material examined. 
Orthite has already been reported by Messrs. Hobbs, Cross and 
Iddings from two of the rocks examined, viz., the granite of Ilchester, 
Md. and Vinal Haven, Me. Grains identical in appearance with these 
occur in the granite of Somesville and Hurricane Ils, Me., Batesburg, 
S. C., Burnett, Texas, and the gneiss of Pascoag, R. I. and Endfield, 
N. H. The granite of Ryegate, Vt. may also contain it though the 
grains look more like sphene, which mineral probably occurs also in 
some of the other rocks mentioned, although with the material at hand 
it cannot be positively distinguished. In the Brazilian rocks orthite 
has been found in the granite of Itaquy in Sao Paulo and the gneiss of 
Santos, Sao Paulo, and Areal, near Petropolis, Rio de Janeiro. In all 
of these localities the mineral disappears on the decomposition of the 
rock, which is probably the reason that it has not been more generally 
met with, since most of the washings have been made on decomposed 
material. All the Brazilian, and apparently the greater part if not all 
the American, rocks affording orthite carry hornblende which, in the 
case of Areal at least, has been in great part altered to biotite. There 
is thus apparently a relation between the presence of hornblende and 
the crystallization of the elements of the cerium group as a silicate 
instead of a phosphate as monazite, the usual form in the purely 
micaceous rocks. That this is not due to the absence of phosphoric 
acid is proved by the presence of apatite in all the rocks examined, 
