MAGNETIC OXIDE OF IRON. 
89 
21 . 
beneath the adjacent rock, if appearances are not deceptive. If so, it is a step towards proving 
the diversity of materials in the earth, and accounting for the greater gravity of the earth as a 
whole, than that of its crust. 
So little can be determined by observation, that reliance cannot be placed on speculations 
of this kind. The naked fact is, that after tracing the ore continuously for five or six hundred 
feet, it disappears under the rock of the country, How far it extends, and what is the nature 
of the termination, cannot be known until the upper rock is removed. Neither do we know 
much in relation to its depth, from actual inspection ; for none of the masses in this region 
have been penetrated more than twenty or thirty feet. But in this distance, two important 
facts are revealed : 1st, that the ore becomes purer and richer; and 2d, that portions of rock. 
22 . 
Mass of fine-grained ore at Adirondack. 
which projected into the mass, disappear. I have, in the annexed diagram, represented this 
fact, as it appears in one of the excavations at Adirondack. The mass often presents the 
appearance of stratification, being divided by planes into layers from four to ten inches thick, 
parallel with which is the layer of rock b. This layer, however, was thicker at the surface, 
Geol. 2d Dist. ' 12 
