120 



action of the weather, into plates, which are rarely 

 continuous, as in the schistose structure, and still 

 more rarely admit of subsequent division. 



The lamellae are either straight, or carved in 

 one or more directions, or contorted. 



They vary in dimensions, from the thickness 

 of many yards down to an inch, and even to that 

 of paper. There are thus a large and a small la- 

 mellar structure ; and the former may be identi- 

 cal with the bedded or pseudo-stratified disposi- 

 tion, as already remarked. 



They are sometimes persistent for a consider- 

 able space ; and, at others, are very limited ; being 

 divided at short intervals by joints. In such cases, 

 they assume prismatic, and even cuboidal forms, 

 so as to become confounded with those of the pris- 

 matic structure. 



The lamellar is thus sometimes united to the 

 prismatic structure, by the latter being an acci- 

 dent of the former. In other cases, they are com- 

 bined in another manner, in consequence of a la- 

 minar structure of the prisms ; as is pointed out 

 Tinder another title. 



It is also occasionally united to the spheroidal 



