Geological Society of London. 47 
that is to say, the rock passes more or less into the “ mylonitic” 
condition. 
(3) That next (probably owing to the action of water under great 
pressure) certain of the constituents are decomposed or dissolved. 
(4) That in consequene eof this, when the pressure is sufficiently 
diminished, a new group of minerals is formed (though in some 
cases original fragments may serve as nucle). 
(5) That of the more important constituents hornblende is the 
first to form, closely followed, if not accompanied, by epidote; next 
comes biotite (the growth of which often suggests that by this time 
the pressure is ceasing to be definite in direction), and lastly a water- 
clear mineral, probably a felspar, perhaps sometimes quartz. 
(6) That in all these cases the hornblende occurs either in very 
elongated prisms or in actual needles. 
The author brings forward a number of other instances to show 
that this form of hornblende may be regarded as indicative of 
dynamometamorphism; so that rocks where that mineral is more 
granular in shape (cases where actinolite or tremolite appears as 
a mere fringe being excepted) have not been subjected to this 
process. 
3. “On a Secondary Development of Biotite and of Hornblende 
in Crystalline Schists from the Binnenthal.” By Prof. T. G. Bonney, 
DiS. HL.D;, ER.S., V.P.G:s. 
Both the rocks described in this communication come from the 
Binnenthal, and were obtained by Mr. J. Eccles, F.G.8., in the 
summer of 1891. They belong to the Dark-mica schists described 
by the author in former papers, and have been greatly affected by 
pressure. In each a mineral above the usual size has been subse- 
quently developed. In the rock from near Binn this mineral is 
a biotite; the dimensions of one crystal, irregular in outline and 
having its basal cleavage roughly perpendicular to the lines indi- 
cative of pressure are about 175” x03", The other mineral, from 
the Peak of the Hohsandhorn, is a rather irregularly formed horn- 
blende, the crystals (which lie in various directions) being sometimes 
more than half an inch long. The exterior often is closely asso- 
ciated with little flakes of biotite. The author discusses the bearing 
of this fact, and the circumstances which may have favoured the 
formation of minerals, so far as his experience goes, of an exceptional 
size. 
Some remarks also are made on the relation of these structures 
developed in the Alpine schists to the various movements by which 
these rocks have been affected, and on the general question of 
pressure as an agent of metamorphism. 
4. “Geological Notes on the Bridgewater District in Hastern 
Ontario.” By J. H. Collins, Esq., F.G.S. 
The plateau of the Bridgewater district consists chiefly of gneiss 
and mica-schist, with subordinate beds of white marble, quartz- 
conglomerate and quartzite, and some veins of ‘‘giant-granite.” The 
general dip of the gneissose series is eastward. 
The author notes the effect of frost in splitting off flakes of the 
