362 Dr. A. Wilmore—Uralite and other Amphiboles. 
the unstable nature of the minerals of the basic rocks. The felspars 
are found changed into saussurite, the augites into hornblende, the 
olivine into serpentine and magnetite. Still further changes may 
have taken place by which the rock is converted into hornblende 
schist or gneiss. 
Almost contemporary with this important series of papers were 
several contributions by Dr. Teall. Of these the first was an oft- 
quoted paper on the Metamorphism of a Dolerite Dyke into a Horn- 
blende-schist.1 At Scourie in Sutherlandshire occurs a dyke of 
hornblende-schist, which is clearly the result of metamorphism of 
a dolerite. In this paper Dr. Teall made a number of very important 
observations relative to such questions as the various stages in the 
development of the secondary hornblende and the production of 
foliation. 
Of the two minerals, augite and hornblende, the former appears 
to be the stable form at high temperatures, the latter at low 
temperatures, ‘“‘so that any condition tending to facilitate molecular 
readjustment must necessarily tend to facilitate the change from 
augite to hornblende. The enormous pressures brought into operation 
in the process of mountain-making may not unreasonably be supposed 
to supply such conditions.” 
Analyses of the dolerite of the hornblende-schist are given, but 
apparently the only safe conclusions from percentages which are very 
similar in the two cases are— 
(1) That the change has almost been one of simple paramorphism. 
(2) That there may have been some conversion of ferrous into ferric oxide. 
= if HelO!> =. Anema (eS Hornblende- ( FeO . Pieri ((i 
Dolerite { ire, Oe a so dchish  \(Blas'O) nena 
In a paper dealing with some minerals from the Lizard,? Dr. Teall 
described a (probably) secondary hornblende, a very pale variety 
occurring in a gabbro-schist at Pen Voose. This was analysed by 
Mr. J. H. Player. 
Si Oz ; - 48°8 CaO : , 12:2 
Ale O3 a 10°6 MgO c 18°6 
Fez O03 ile7 Ignition loss 1°8 
FeO 4:7 
On this analysis Dr. Teall remarks: ‘‘If this hornblende be 
secondary, then its composition does not bear out the view that 
secondary hornblende is derived from pyroxene by a paramorphic 
change.”’ 
In 1885 Dr. Hatch? described gabbros passing into amphibolites, 
the alteration series being— 
Normal gabbro, hornblende gabbro, amphibolite, epidote rock. 
Another alteration series is suggested, as follows :— 
Normal gabbro, uralite gabbro, actinolite or nephrite-schist, serpentine. 
1 Quart. Journ. Geol. Soc., 1885, vol. xli, pp. 133-45. 
2 «« Notes on some Minerals from the Lizard ’’: Min. Mag., 1888, vol. viii, 
p. 116-20. 
3 « Uber den Gabbro aus der Wildschnonau in Tyrol,” etc.: T.M.P.M., 1885, 
Bd. vii, pp. 75-87. 
