SO Ga Willams—-Pyronene and Hortblandle 
in structure, had evidently resulted from a gradual and often E 
incomplete molecular change of crystals originally altogether 
augite, just as monoclinic crystals of sulphur may be observed _ 
found to be exceedingly wide spread. 
It is generally conceded that temperature is not the only 
influence which conditions the crystalline form assumed by the 
pyroxene-hornblende molecules. Hornblende is often observed 
as a primary constituent of certain (generally acid) lavas, and it 
seems probable that augite may be formed at comparatively 
low temperatures. e chemical constitution of the mass in 
which the crystals are formed, as well as other conditions not 
in the region about Baltimore.”* In a large majority of cases 
the change seems to be to true uralite. Hypersthene and 
by Baldauf, 1883. 
10 F, Becke: Tschermak Min. und Petr. Mitth., 1882, p. 157. 
1 J. Lehmann: Die altkrystallinen Schiefergesteine. Bonn, 1884, P- 190. 
2 Of, A. Geikie in “ Nature,” June 5th, 1884. ee 
13 G, W. Hawes: Metadoleryte from Littleton, N. H. This Journal, IU, xi, P- 
136. 
14 R, D. Irving: this Journal, July, 1883. 1 198k 
18 G. H. Williams: Johns Hopkins University Circulars, No. 30, April, 18°* 
