210 Prof. T. G. Bonney—Quarlz-Schists from the Alps. 
Again, though these quartzites, just enumerated, are separated 
from the quartz-schists by distinctive characteristics, we find occa- 
sionally rocks which may be said to occupy an intermediate position. 
Of these I possess only a few examples. Some of the Huronian 
quartzites, which show no signs of pressure, are now quartz-mica 
rocks, in which, as I have said,’ we cannot determine what portion 
of either mineral is allothigenous, and are led to believe that their 
present forms were assumed in situ. I have found the same structure 
in a pebble from the basal Cambrian conglomerate at St. David’s,” 
and may add that small fragments of quartz-schist are often not 
uncommon among the oldest coarse grits and conglomerates. 
But on grits and shales which have been exposed to the action of 
important earth movements—such as those which come from the Alps 
themselves—pressure has produced but moderate effects. Certain 
of the more minute constituents have undergone micro-mineralogical 
change; but, generally, of the larger constituents, though certain of 
the more unstable have been altered, most of them are little affected ; 
even fragments of organisms can still be recognized. In the 
crystalline masses, zones doubtless occur, here and there, where 
the effects of crushing are very conspicuous; where, for instance, 
granitic rocks have been converted into fissile fine-grained mica- 
schists; rocks also there are (such as some of the pyroxenic group), 
the constituents of which seem exceptionally unstable under pressure, 
but many large masses are comparatively little affected. On what 
grounds, then, when the sedimentary rocks have emerged from the 
pressure with so little loss of personal identity, are we justified 
in assuming that the crystalline masses have been completely re- 
constituted, and that the cases just mentioned, instead of indicating 
the extreme effects of pressure, represent really its partial effects, 
that is to say, where crushing has been followed only by partial re- 
constitution. For any such assertion I cannot find the slightest 
grounds in the Alps. 
So the specimens of quartz-schist discussed above (1) give no proof 
that their structure was caused by pressure; (2) show that if they 
have been crushed, great molecular changes have since occurred ; 
(3) afford indirect proof that their structure is pre-Tertiary ; (4) are 
not like Palaeozoic rocks which have been crushed. In short, pressure 
is a most important agent of change, but it is far from being the 
only one. Dynamometamorphism is a fine-sounding term, but 
“comfortable words” are more suited for old women than for 
scientific men. 
associated with crystalline schists. Also the quartz-schists in the district near 
Braemar ; some of which occur near to cale-mica-schists, very like those of the Alps, 
others pass into mica-schists or a kind of gneiss. In microscopic structure both rocks 
agree in the main with these Alpine quartz-schists. The gneissoid bands seem likely 
to confirm the idea expressed above that one kind of gneiss may result from the 
alteration of a quartz-felspar grit, but I must verify some points before I can venture 
to say more. 
1 Q.J.G.S. vol. xliv. p. 32. 
2 Grou. Maa. Dec. ILI. Vol. VI. (1889), pp. 312-318. 
