HORIZONTAL ARRANGEMENT. 



FIG. 73. 



VERTICAL COLUMNS. When basaltic columns .occur in 

 tabular masses, as at the Giant's Causeway, or Stafia, they 

 are commonly vertical, as in fig. 74. 



FIG. 74. 



HORIZONTAL ARRANGEMENT. "When they occur in dikes, 

 and have been erupted through overlying masses, they are 

 usually smaller, and take a horizontal position, owing, in all 

 probability, to the force with which they have been urged 

 upwards, and the resistance which they have met* with from 

 the deposits which they have penetrated, as in this fig. 75. 



FIG. 75. 



