I §4 MINERALOGY AND LITHOLOGY. 



found to be in perpetual motion. Tliey 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 in a 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 



