1882.] ^'J'^ Gcnth. 



iind shows a large cleavage angle, similar to ampliibole ; the termiiml 

 planes are either not developed or broken oft. It incloses, like the original 

 talc, grains of chromite. Its Spec, gravity was found to be 2.983. Besides 

 my analysis (a) I will give, for comparison, the analysis by Dr. A. Brezina 

 of the authophyllite from Hermannschlag in Moravia (Tschermak's 

 Mineral. Mitth.,\8T4, 247). 



Castle Rock. riermannschhiL--. 



SiO, =: 56.88 — 57.39 



ALA ^ 2.45 — 2.04 



CrjOs = trace — 



FCaO., = — 0.42 



FeO = 9.20 — G.53 



MnO = 0.28 — 



NiO = 0.17 — 



MgO = 28.50 — 29.08 



CaO =r — 0.69 



Na.p z= 0.18 — 



K^O = 0.03 — 



Ignition = 2.28 — 2.56 



99.97 98.71 



From the description of the mica globules from Hermannschlag, by Di- 

 rector G. Tschermak (Tschermak's Min. Mitth., 1872, 264) we learn that 

 next to the anthophyllite-stratum and between it and the nucleus of biotite, 

 is a stratum which has a seladon-green color, and appears to be a mixture of 

 talc and chlorite, strongly altered. This observation is of very great 

 interest in connection with the evident alteration of talc into anthophj-l- 

 lite, above described. 



There is also an observation of Dr. F. Becke (Tschermak's Min. Mitth. 

 [ISTeue Folge] iv, 450) w^ho noticed the alteration of olivin into authophyl- 

 lite between the gabbro locality "Yier Linden" and the R. R. Station 

 Rossw'ein in Saxon3^ The olivin shows in many places a commencing 

 alteration into serpentine (or talc ?), and is surrounded by a stratum of 

 anthophj-llite of from 5-6'"™ in thickness. This seems to be an analo- 

 gous case, first, the olivin altered into serpentine {or tatc), and this subse- 

 quently changed into anthophyllite. 



IV. Talc, pseudomorphous after Magnetite. 

 In the vicinity of Dublin in Harford county, Md., is a series of rocks, 

 consisting principally of gneiss and micaceous schists. They are under- 

 laid by a bed of talcose slate, changing in some places into a very superior 

 quality of massive soapstone, from 12 to 15 feet in thickness. Immediately 

 adjoining, and under the talcose slates and soapstone, and in most cases 

 separated from them by seams of chlorite or chlorite slate, lies a very 

 large bed of a beautiful variety of green serpentine, mottled and of darker 

 and paler green colors, of about 500 feet in thickness, and under this, a bed 



PROC. AMER. PHILOS. SOC. XX. 112. 2x. TRIXTED NOV. 8, 1882. 



