184 MINERALOGY AND LITHOLOGY. 
found to be in perpetual motion. They dance about, and move most 
irregularly from side to side of the cavity, as though acted upon by some 
very erratic power, These movements are referred to the same cause as 
the so-called Brownian movements of fine suspended matter, and have 
been explained in various ways. They are by some supposed to be 
caused by the constant molecular movements that are believed to take 
place in all fluids; by others, they are supposed to be caused by a 
vibration or jar, which, though inappreciable to our senses, thus evinces 
itself to be ever active; by others, they are referred to the action of light, 
or are to be explained in the same way as are the movements of Crooke’s 
radiometer. The motions referred to, which can be seen in any of our 
porphyries and granites, are certainly curious and interesting; but the 
phenomenon is a physical one, and has no geological significance. The 
lack of a satisfactory explanation will not therefore be felt. Zirkel re- 
marks, that whatever may be the cause, it is an interesting thought that 
these bubbles, in number approaching infinity, have been dancing about 
during all the ages since the rocks were made. Unless it shall be shown 
that they are influenced by light, and that their movements therefore 
date from the time that the sections were made, it certainly is a strange 
thought to think of so much motion ina lifeless mass. 
The region of Mt. Pequawket is a very interesting one in which to 
study the quartz porphyries, owing to their singular relationships to the 
surrounding rocks. At this point there are accumulations of clay slates; 
but at some places on the mountain they are all broken up, and again 
consolidated, so that they form an immense great breccia most striking 
in aspect. At some points which are characterized by this destruction 
of strata, the breccia is wholly of angular fragments of slate; at others, 
felsite and quartz porphyry form the cement which binds the fragments 
together; at other points, fragments of slate are sparingly distributed 
through the massive quartz porphyry. The region is, I think, considered 
a remarkable one by all those geologists who have visited it. It seems 
to be plainly indicated that here was the seat of some grand disturbance 
that resulted in the destruction of the strata of slate, and the eruption of 
quartz porphyries into the fissures made. Now, when the cavities in the 
minerals of plainly eruptive masses of porphyry or granite are examined, 
they show the same identical features as do others which appear to be 
