194 USI BIL (Cy IRS SVRILIL 
Missouri Buttes, is phonolite, instead of sanadine-trachyte, the 
conspicuous feldspar being ‘‘soda-orthoclase or anorthoclase.”’ 
A chemical analysis of the rock gave SiO, 61.08, and Al,O, 
18.71. ‘A vertical dike about fifty feet wide, cutting through 
the schist and Palzozoic series in the mountains south of Dead- 
wood,” observed by C. E. Beecher, is also mentioned. 
Observations by W. M. Dawson, W. H. Weed and L. V. 
Pirsson, seem to show that domes with cores of plutonic rock 
and surrounded by horizontally stratified beds, similar to the 
domes with plutonic plugs in the neighborhood of the Black 
Hills, form the Sweet Grass Hills and Zogo Peak, Montana.* 
Errata.—The titles of Figs. A and B, Plate II., Vol. IV. of 
. this JouRNAL, should be transposed. The title for Fig. A should 
read, ‘‘Little Missouri Buttes from the East.”’ 
ISRAEL C. RUSSELL. 
™* Report upon Country in the Vicinity of Bow and Belly Rivers, Northwest Terri- 
tory, in Geol. and Nat. Hist. Sur. and Mus. of Canada, Report of Progress, 1882-3-4, 
c. pp. 16, 45. 
W. H. WEED and L. V. Pirsson, “On the Igneous Rocks of the Sweet Grass 
Hills, Montana,” in Am. Jour. Sci., Vol. L., 1895, pp. 309-313. 
L. V. Pirsson, “On Some Phonolitic Rocks from Montana,” in Am. Jour. Sci., 
Vol. L., 1895, pp. 394-399. 
W. H. WEED and L. V. Pirsson, “Igneous Rocks of Zogo Peak, Montana,” in 
Am. Jour. Sci., Vol. L., 1895, pp. 467-479. 
