1894. ] NEW YORK ACADEMY OF SCIENCES. 141 
The late Prof. G. vom Rath,* to whose travels in this coun- 
try in 1884 we owe many acute and interesting observations on 
western localities and mines, noted at Rattlesnake Bar, El 
Dorado Co., Cal., an orbicular diorite, which he describes as of 
exceptional perfection. -It is much the same thing as the Cor- 
sican occurrence but has the radiating structure less promi- 
nently formed. Zirkel+ also records a tendency of quartz, 
feldspar and muscovite to form minute zones around magnetite 
crystals, in a granite from Clark’s Peak, Medicine Bow Range, 
Colorado. 
Four years ago, the writer obtained some fragments of orbi- 
cular granite of exceptional perfection, while visiting the quar- 
ries at W esterly, Rhode Island, but did not ascertain until last 
summer the exact locality. It was then learned that they were 
taken from a boulder at Quonochontogue Beach. This is sit- 
uated in southwestern Rhode Island, about eight miles east of 
Watch Hill, and five miles south of the nearest railway station, 
Niantic, on the shore line for Boston. The place is thus 
quite inaccessible, but nevertheless 2 few cottages and a small 
hotel have sprung up. On visiting the locality the boulder was 
found to be about 6 feet by 5 feet by 4 feet, and to be one of a 
number making up an old glacial dump. Half of it is orbicu- 
lar and half normal biotite- granite or granitite of rather coarsely 
crystalline structure. The : granitite is, however, just the same 
as is found in neighboring ledges, and is only a coarser variety 
of the one which is so extensively wrought at Westerly and 
Niantic. The boulder has not been transported far, but in all 
the outcrops seen, no orbicular structures have been met in 
place. This whole coast is formed of drift, mostly coarse mo- 
rainic material, and except for the ledge referred to no other 
exposure appears for several miles to the north. The surface 
consists of morainic hills, with great sandy or gravelly stretches, 
which mask the underlying ceology. It is possible that the 
parent ledge of the boulder may yet be discovered, but it is 
hardly probable. 
The normal granite is mainly composed of quartz, orthoclase, 
and biotite, with considerable plagioclase as well. It is a very 
pure biotite granite or granitite. A few stray magnetite grains 
appear, and a zircon or two in each slide. 
The nodules run from 2-3 inches (5-7 cm.) in diameter and 
are rudely elliptical in outline. The center consists quite en- 
tirely of plagioclase, but a few quartzes may be recognized 
*Sitzungsberichte der Niederrhein. Gesellsch. f. Natur. und. Heilk. zu 
Bonn., December 1, 1884. 
t+ For'ieth Parallel Survey, Vol. VI., p. 54, 1876. 
