ESSEX COUNTY. 285 



The above remarks apply to the sand and gravel beds situated in the upper valleys of the 

 Adirondack mountains, upon their less sloping sides, or where the inclination is only mode- 

 rately steep. I find, however, in some of the deep depressions, where there are natural 

 meadows, beds of claj'-, analogous to the porcelain clay from the ordinary varieties of granite. 

 The hyperslhene rock, like that of the granite of Johnsburgh, disintegrates, and finally de- 

 coni])oscs ; the alkali leaving the aluminc and silex of the feldspar, a complete separation of 

 the elements ensues. The clay which results from this decomposition, collects slowly in those 

 depressions which are favorably situated. These beds are found in the midst of the Adiron- 

 dack mountains, where they are from eighteen hundred to two thousand feet above the level 

 of Lake Champlain. No analysis has yet been made of this variety of clay, but probably 

 the proportions of silex and alumine will not differ very materially from those of the common 

 porcelain clays. From this clay an excellent brick has been made, which possesses yery re- 

 fractory powers : it at least has one property which is quite important, viz. that of remaining 

 sound wli^n dried in the sun or fire, and it may be heated suddenly w-ithout breaking or flying 

 to pieces. The color is light blue, or bluish white ; but I have never observed it a pure white, 

 neither does it become white by burning: the bricks arc yellowish after burning. It is not 

 so tenacious as the tertiary upon the lake, and does not adhere so obstinately to substances 

 put into it ; still it is ductile, and moulds well. I am inclined to believe that this clay is 

 adapted to a variety of purposes ; but as it has only been employed for brick, my belief is 

 only a matter of opinion. Its fineness, and ability to stand high degrees of heat w'ilhout melt- 

 ing, but more than all its freedom from cracks when dried or burnt, impart a value to it above 

 all ordinary clays. In the use of it for fire-brick, however, it is necessary that it should be 

 employed with a pure siliceous sand. The sands and gravel in the immediate neighborhood 

 being made up of a great amount of feldspar, operate as a flux to the clay, and w'ill cause it 

 to melt. It will be much better to employ it without sand, unless it be one composed purely 

 of silex. 



Simple Minerals. 



The names of many of the simple substances have already been given ; a brief repetition, 

 however, is necessary in order to exhibit the mineral riches of this county in their true light. 

 Those which occur in the condition of rocks, may be put first : 



1. Labradorite. This substance has not yet fallen under my notice under any form except the primary, 

 and under cleavage planes. In this respect, it is analogous to the feldspar which forms the consti- 

 tuent of ordinary granite. 



2. Calcareous spar, or Carbonate of lime. Very few localities where it is crystallized. One of the 

 most interesting varieties is the blue of Long pond. 



3. Magnetic oxide of iron. The same remark is called for in regard to its crj^stallization, as in the 

 preceding substances. It is uncrystallized, except in the mass. Not a single crystal has fallen 

 under my notice during the survey, though I have examined very carefully all the mines in the 

 county. 



