LITHOLOGY. 221 
by him in his report on the geology of Massachusetts. Subsequently, 
aided by his son (the chief of our survey), the subject was more thor- 
oughly investigated by him, and it was found that the flattening of pebbles 
between layers of schistose rocks had taken place at many localities, and 
that a geological significance was to be attributed to the circumstance. 
Since that time analogous phenomena have been found all over the 
world, so that it is no longer a novelty; but it is well understood that 
pebbles of quartz, or of other substances, may be variously altered in 
form by the processes of rock metamorphism, which are not of that 
degree of efficiency that entirely obliterate all signs of the original con- 
stitution of the sedimentary mass. In limestones, well known fossils, 
which are flattened and contorted, are found between the strata; in con- 
glomerates, two pebbles, one of which has forced itself half way through 
its more yielding neighbor, are sometimes found in juxtaposition ; and 
in a mixture of fine and coarse material, the finer part may be converted 
into mica schist, while the pebbles do not enter into the mass, but are 
softened and flattened into thin discs. These facts are again brought 
forward by those who think that the stratification of such rocks is par- 
tially or wholly due to pressure acting at right angles to the plane of 
the lamination; and they point very definitely to the circumstance that 
though, in these rocks now under consideration, the stratification is 
parallel to the original bedding, yet pressure must be considered as a 
very efficient agent in inducing a schistose or finely laminated condition. 
At some places in New Hampshire the strata of the schistose rocks 
are most curiously broken. On Mt. Pequawket a huge breccia occurs, 
which is composed of large broken and angular fragments of argillitic 
mica schist. These fragments lie in all directions, and at all angles with 
one another, but are firmly consolidated into a compact mass. This is 
not so difficult to understand, for at some other points the fragments are 
found cemented together by a felsitic mass, and at others quartz por. 
phyry constitutes the bulk of the rock, and in it the fragments of schist 
lie embedded. It therefore appears that the strata of schist were crushed 
and broken by the force that opened a way for the eruption of the 
quartz porphyry, which forms a large part of the mountain. But the 
cause of the broken condition of these schists is not always so plain. 
In the south-western part of the state, such appearances are not rare 
