Geology. 478 
neighborhood of C the dispersion is nearly the same as would 
be given by four prisms. 
The spectra of the higher orders are generally not so well 
seen on account of their overlapping each other, but fortunately 
with one particular adjustment of the angle between the collima- 
tor and telescope, the C line in the spectrum of the third order 
can be made to fall in the vacant space between the spectra of 
the second and fourth orders, and we thus obtain an available 
dispersion nearly the same as that of the instrument I am 
accustomed to use. 
On applying the new instrument to the equatorial, I found 
(under atmospheric conditions by no means favorable, though 
the best that have presented themselves as yet), that in the first 
order spectrum I could easily see the bright chromosphere lines 
, D,, and F; I could also, though with great difficulty, make 
out Hy, (2796 K). On opening the slit the outline of the chro- 
mosphere and the forms of the prominences were well seen, 
both in the spectra of the first and third order, quite as well 
I think as with my ordinary instrument in the same state of the 
air. The spectra are of course fainter, but as this loss of light 
affects the back ground upon which the prominences are pro- 
jected, as well as the objects themselves, it does not materially 
injure their appearence. 
The grating is much lighter and easier to manage than a train 
of prisms, and if similar ruled plates can be furnished by the 
Opticians at reasonable prices and of radars quality, it 
would seem that for observations upon the chromosphere 
and prominences they might well supersede prisms. 
College, May 9, 1873. 
SCIENTIFIC INTELLIGENCE. 
I. GEOLOGY. 
b: 
officers of H. M. Surveying ship Hecate brought to the office of 
the California Survey a slab hich had bee et 
somewhere up the coast far to the north of San Francisco, but the 
exact locality of which I was unable to ascertain, as the specimen 
was in my absence. The slab was to me ly interest- 
ing as it closely resembled, both lithologically and paleontologi- 
ly, our Plumas County Triassic slates.* Indeed the specimen 
looked so familiar that for some time I could hardly convince 
myself that there was not some deception about it. 
* See Geol. of Cal., Vol. i, p. 309. 
