378 J. P. Kimball on the Geology of Western Texas. 
is the réversal of a well marked though not prominent line just 
below E, put down as iron by both Kirchoff and Angstrom, 
though not given by Huggins. Whether the position of the 
apparently coincident Aurora line is as well settled I am not 
yet certain, but hope to be able to ascertain before very long 
by a direct comparison between the spectrum of the Aurora 
and that of the electric spark from iron electrodes. At pres- 
ent it seems pretty likely that the spectra of the corona and 
the aurora borealis are identical with only such differences in 
the intensity of their lines as we might naturally expect, and 
that very probably the identity extends to the essential nature 
of the phenomena themselves. 
Should it turn out that this line in the aurora does actually 
coincide with 1474, it will be of interest to inquire whether we 
are to admit the existence of iron vapor in and above our at- 
mosphere, or whether in the spectrum of iron this line owes its 
presence to some foreign substance,—probably some occluded 
gas as yet unknown, and perhaps standing in relation to the 
magnetic powers of that metal. 
Hanover, N. H., Sept. 13, 1869. 
The above article comprises the substance of two papers read 
at the last meeting of the American Association for the Ad- 
vancement of Science at Salem. 
Art. XXXVIL—WNotes on the Geology of Western Texas and of 
Chihuahua, Mexico; by JAMES P. KIMBALL, Ph.D. ‘a 
THE road from San Antonio, Texas, to Presidio del Norte on 
the Rio Grande, by way of Fort Clark, Camp Stockton and 
Fort Davis, traverses the elevated Cretaceous table-land of west- 
valleys, the streams have repeatedly changed their beds, most 
of ou a are dry except in gee of heavy rain. The grassy 
