84 J. D. Dana on the Quaritzite, Limestone, etc., 
be possible, not only to settle this question of identity with the 
air-spectrum, but also to get some approximate ideas upon the 
temperature and pressure in the auroral regions, and to deter- 
mine the reasons of the differences observed in the spectra of 
various auroras. Pocket-spectroscope examinations may give 
a general idea of the spectrum, but they cannot serve for any 
exact determinations.* 
New Haven, Dec. 30, 1872. 
Art. X.—On the Quartzite, Limestone and associated rocks of 
the vicinity of Great Barrington, Berkshire Co., Mass.; by 
JAMES D. DANA. 
[Continued from page 53.] 
2. From the Housatonic valley westward— continued. 
In the ridge (L) to the southwestward of Housatonic village, 
the quartzite stratum, instead of being replaced by mica slate, as 
is the case to the north and northwest, is quartzite still ; more- 
over, the underlying stratum of gneiss, s!, is quartzite also, $0 
that the limestone—the outcropping rock of Long Pond valley 
—is directly overlaid by quartzite. Further, these rocks, 2 
place of being nearly horizontal in position, are nearly vertical. 
Figure 6 represents an east and west section across this 
region a mile north of Vandeusenville, and extending west 
through the Tom Ball ridge into Alford.+ (Fig. 3, of a sec 
tion through Williamsville, and 5, of one through the north 
* An examination of the spectrum of this aurora with Hawkins and Wale’s 
direct-vision pocket spectroscope showed that it coincided apparently with yo 
spectrum seen in the larger instrument, except that the bands were not 
the less di 
+ Above V4, in the section fig. 6, is the Tom Ball ridge; above A‘, the Long 
Pond valley ; above L, the ridge L; at W, Williams river; at H, the Housatonie 
river, with low plains either side. 
