102 



GEOLOGY OF THE THTRD DISTRICT. 



18. 



■Il IMlf •' 



No. 1. A aingle hopper-aliaped form from Bulls' quany, town of Lenox, Madison county, and resembling those which are formed 



upon the surface of the aolar salt pans. 

 No. 2. Exhibits three of the same forms, being one-half of a cube, their apex pointing to a common centre ; from Kelly's quarry 



in the same town. 

 No. 3. Shows a congeries of hoppers disposed in a line, the specimen from Bulls' quarry in Lenox. The line which crosses 



the range of crystals or forms, shows they were formed when the mass was in a measure desiccated or dried. 



Hopper-shaped Cavities. The most interesting of all the products of the group are the 

 hopper-shaped forms and cavities, the wood-cut showing three different appearances of them. 

 These forms and cavities are of great importance, for they were produced by common salt, 

 no other common soluble mineral presenting similar ones. They show that salt existed in 

 the third deposit, and the position which they hold in the deposit should regulate all future 

 borings that may be made for rock salt. These cavities are in shape like a mill hopper, 

 whence their name. When salt is observed to crystallize, a cube first makes its appearance 

 upon the surface of the brine ; this sinks gradually, as a series of similar cubes form around 

 its outer border, being attached to its upper surface near its edge. When those are com- 

 pleted, the whole sinking as additional particles are added, another row of cubes are formed 

 upon the first range ; and thus for many repetitions, until the density of the mass formed becomes 

 greater than the liquid, when it falls to the bottom. When examined, being turned upside 

 down, it shows a pyramid of regular steps, terminated by a cube ; and when its position is 

 reversed, a form like the hopper of a mill : its perfection depending, as in all other cases, 

 upon the absence of interfering or disturbing causes. No. 1 of the wood-cut shows a single 

 pyramid or hopper, but the cubic arrangement is wholly indistinct. 



In all the localities where two ranges of plaster beds are seen, the hoppers occur between 

 them, and between the two masses of vermicular rock : they are from one to three and more 



