284 Reports and Proceedings—Geological Society of London. 
quartzites into quartz-schists; the limestones become crystalline ; 
the sheets of intrusive felsite, diorite, and granitoid rock pass into 
sericite schist, hornblende-schist, and augen-gneiss respectively. 
The researches furnish a vast amount of evidence in support of 
the theory that regional metamorphism is due to the dynamical and 
chemical effects of mechanical movement acting on crystalline and 
clastic rocks. It is also clear that regional metamorphism need not 
be confined to any particular geological period, because in the N.W. 
Highlands, both in Pre-Cambrian time and after the deposition of 
the Durness Limestone (Lower Silurian), crystalline schists and 
gneiss were produced on a magnificent scale. 
2. «On the Horizontal Movements of Rocks, and the Relation of 
these Movements to the Formation of Dykes and Faults and to 
Denudation and the Thickening of Strata. ” By William Barlow, 
Hsq., F.G.S. 
The paper commenced with a description of some horizontal move- 
ments of rocks caused by gravitation; and the author quoted Mr. C. 
EK. Dutton’s descriptions of the Grand Cafion District, especially 
noting the fact that between succeeding escarpments the strata dip 
slightly from the crest of the one below to the foot of the next above, 
and that whilst the strata of the median parts of each terrace are 
nearly horizontal, the inclination increases as we approach the 
escarpment of the next higher terrace, and also that Dutton observed 
indications of a slight elevation of the unloaded strata within the 
denuded elliptical area known as the “San Rafael Swell.” After 
alluding to Dutton’s suggestion that the phenomenon referred to is 
analogous to the action “of creeping in deep mines, the author dis- 
Cagced the nature of such “ creeps,” which he deared as the thicken- 
ing of the parts of beds from which a load of superincumbent rock 
has been lifted, caused by a thinning of the adjoining parts which 
remained loaded, some of the substance of the latter having been 
squeezed out to furnish the material for the thickening, and suggested 
that some of the subsidiary plications found on the flanks of moun- 
tains are caused by the thrusts arising from creeps. He also paralleled 
the fissures in the precipices of the Grand Cation District with those 
produced in the pillars of coal owing to the strain induced by the 
slight inequality in the yielding of the bed supporting it, and pointed 
out how such fissures would facilitate denudation, giving instances 
recorded by Dutton, and that an appreciable influence might be thus 
produced in all cases of mountain-denudation. 
The author next considered the case of a body of molten rock 
below a considerable mass of solid rock. The pressure upon the 
molten mass would cause movement to take place towards the point 
where the superincumbent weight was least, provided that absolute 
equilibrium did not exist. The overlying rocks being more or less 
plastic, some horizontal movement of the solid rocks at the confines 
of the molten mass, and subjected to its influence, might be looked 
for. Any such yielding would tend to draw apart the solid crust 
resting upon the molten rock, and the ground would open along lines 
of weakness, such as would be produced by the presence of joints, 
the crust in some cases breaking up into larger or smaller fragments. 
