22 J. C. Draper—Projection of the Fraunhofer Lines 
The ‘ci al sion is a species of syenite of moderately fine 
texture. It contains a ground mass o cya ne granular red 
feldspar, Pees pepuey tes and magnetic iron. In this occur 
porphyritically larger crystalline eas of red feldspar and 
quartz. e slates sometimes form a peculiar rock, indicating 
a gradual passage from slate to syenite, owing to contact effects. 
These portions might sometimes be mistaken for conglomerates, 
since pons nob rounded nodules of red feldspar and Hee 
which exactly resemble water-worn pebbles. ey he im- 
bedded in se matter, but perfectly distinct from it. We thus 
see that the structure ‘bere; is precisely the same with that at 
Harper’s Ferry. e central mass, however, is true igneous sye- 
nite. In composition it resembles the coarse syenite occurring 
farther southwest, but it is much better crystallized. 
Among the products of metamorphism to be seen in the 
altered slates we may mention the following: 1. Rocks so 
highly impregnated with epidote as to appear a mass of acicular 
— s. 2. The formation of numerous concretions of the size 
a buckshot, composed “4 a core of epidote, with an envelope 
of milk- white uartz. 8. Cale spar with the characteristic 
cleavage. is is oe intimately associated with 
epidote and ‘ilk fibers of asbestos, the spar being colored green 
by finely-disseminated hornblendic matter. 5. Masses of car- 
bonate of lime, having a fine saccharoid texture like alabaster, 
and much like enclosed and metamorphosed fragments of ordi- 
nary limestone. They are, however, impregnations. Interesting 
studies both of the regen eg and paragenesis of metamorphic 
minerals may be obtain 
The contact of the Silutias with the argillite is beautifully 
exposed in the west entrance of the tunnel, and the great con- 
trast of the two systems thus brought side by side is well 
shown. 
[To be continued. ] 
Art. IIL—Projection of the Fraunhofer Lines of Diffraction ce 
Prismatic Spectra on a Screen; by Prof. Joun C, DRAPER 
College of the City of New York: 
Havine been engaged during the past year in making photo- 
graphs of absorption spectra of organic bodies, in which a solar 
spectrum with Fraunhofer lines was formed by a diffraction 
grating, I have resorted to the following method of forming 
such solar spectra, a description of which r may prove of interest 
to those who are experimenting in the same field. 
