252 PSEUDOMORPHOUS MINERALS OF NEW YORK. 



men the individuals of the rhombohedral iron ore are so minute 

 that they form a compact mass, contained within smooth planes, 

 having the situation of the faces of a regular octahedron." 



Now the change from tlie magnetic oxide to the specular ore 

 is a very slight one, the former containing one atom of protoxide 

 of iron and two atoms of peroxide, while the latter is the pm:e 

 peroxide. Still, although the only difference between these two 

 minerals consists merely in two or three per cent, of oxygen, it is 

 not so easy to account for the change. Whence has the oxygen 

 been obtained by which it was effected? I would suggest 

 whether the protoxide of iron may not have been replaced by 

 some other substance, as lime or magnesia, which has in its turn 

 again been dissolved out. 



To the changes which have thus been noticed, I will only add 

 that which has taken place in some of the strata of red marl in 

 the vicinity of the salines of Onondaga county. There are often 

 observed in these strata hopper-form cavities and crystals, consist- 

 ing of the material of the clay covered with an incrustation of 

 calcareous spar, resembling those crystals of salt formed during 

 an intermission in the application of heat, and commonly known 

 by the name of Smnday salt. About half a mile from the village 

 of Camillus, on the route of the Auburn and Syracuse rail-road, 

 the marly clay is chiefly made up of these crystals, varying in 

 size from one inch to eight inches. They usually have their sur- 

 faces covered with an incrustation of pvue carbonate of lime, and 

 then* bases slightly rhomboidal and variously bent. They indeed 

 appear as if subsequently to their formation, they had been sub- 

 jected to a highly elevated temperature. I analyzed a fragment 

 of one of these crystals and found its composition to be as fol- 

 lows, namely : 



Carbonate of lime, 26.25 



Carbonate of magnesia, ...... 19.35 



Oxide of iron, 4.65 



Silica and alumina, (clay,) ..... 49.75 



From the form of these clay crystals it has been inferred that 

 they were originally crystals of salt. Now whether these were 

 dissolved out by water, and the new material introduced by the 



