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configuration ; but, in reality, it is properly 

 placed here. 



The columnar structure is invariably aggre- 

 gated. No instance, that I know of, has yet oc- 

 curred, of a single column, as there are of single 

 spheroids, included in an amorphous mass. 

 Pitchstone scarcely offers an exception; as the 

 small columns which it sometimes exhibits, are 

 portions of lamellae. 



As the prisms are often accumulated in a pa- 

 rallel manner, of the same length, and for a con- 

 siderable space, they unite to form a bed, or 

 pseudo-stratum ; or else such a bed appears to be 

 split into prisms, and that division generally takes 

 . place nearly at right angles to the leading planes. 

 But as such planes are not necessarily parallel, 

 so, in a mass of prisms, the lengths of these con- 

 cretions will be found to vary in different parts. 



Not unfrequently, the most regular columnar 

 structure vanishes in the same continuous mass, 

 and in a gradual manner. This takes place, 

 either laterally, or in the direction of the axes. 



In a columnar mass, the axes may be vertical, 

 or inclined to the horizon at any angle, or hori- 



