127 



chanical views would account for the length, parallelism, thin- 

 ness, and trough-like arrangement of the plates. 



Dr. Jackson stated as a curious fact, that in the Pudding 

 stone of Roxbury, fissures exist which pass through the 

 pebbles as well as the matrix in which they are enclosed. 



As the pebbles are much harder than the enclosing rock, it is 

 difficult to explain this phenomenon. But in no instance. Dr. 

 Jackson stated, is the pebble loosened and dropped from its bed 

 by the opening of the fissure. In some cases it is broken into 

 three pieces, one remaining imbedded in each face of the open- 

 ing, and the third being locked between them. Dr. J. had 

 observed the same thing in the Pudding-stone of Rhode Island. 

 If these fissures had been produced by contraction of the rock, 

 the pebbles should drop out. In conclusion, he suggested that 

 an earthquake shock might have been the cause of the phenom- 

 enon. 



Prof. Rogers said that he did not believe the appearances in 

 question could be explained by earthquake movements, as the reg- 

 ular forms of the masses bounded by the fissures were at variance 

 with the observed effects of these movements. Nor was he wil- 

 ling to admit any other mechanical cause as sufficient to account 

 for them. He thought that this division was due to a similar 

 cause to that producing slaty cleavage ; some corpuscular force ; 

 a force generated at the place of action, and extending through 

 the whole mass of matter, such as that arising from electric or 

 magnetic attraction and repulsion. 



Dr. Jackson thought that the heterogeneous character of the 

 Pudding-stone precluded the possibility of accounting for the 

 fissures by any general cause such £^Prof. Rogers assigned for 

 them, excepting heat. In reply to a question from Mr. Desor, he 

 stated that the Pudding-stone belonged to a date anterior to the 

 Coal. 



Mr. Desor presented to the Society a new theory to 

 explain the formation of fogs on banks and shoals, which 

 he thought would also account for the formation of ground 

 ice. 



