CHARACTER OF THE METALLIFEROUS VEINS. 
143 
ation, and what is quite as interesting at this locality in Clinton 
county, is the intersection of the rock by several trap dykes. 
The surface of the rock is denuded and shows particles of ore 
disseminated through it, particularly between the dykes; a, a, 
dykes, c, c, the spaces in which ore is sparsely disseminated 
at the surface, at b, the ore increases, and at d, on the other 
side of the 14 foot dyke, it is a solid mass of ore, with scatter¬ 
ing grains of gray quartz. This wide dyke cuts the veins ob¬ 
liquely. The ore was lean on the east side, but much better 
upon the west, as an adit on being cut through it, disclosed 
a mass of ore on the opposite side, seventy feet thick. 
Fig. 30. 
D 
D Adit. 
Fig. 30, is a ground plan of the dykes, showing their relations 
to the ore. These are not parallel, and as they intersect each 
other, they are clearly of different ages. The widest intersects 
the vein of ore, but the narrower ones are intersected by the 
latter. A, vein of ore running N. E. and S. W. B, vein of ore 
which runs nearly east and west. The latter is a rare example 
of a vein pursuing this direction. D, adit. Veins of magnetic 
iron often contain masses of rock in the midst of the ore which 
under certain circumstances have the semblance of walls. 
They are generally pure rock free from the ore, and as they are 
arranged in a direction parallel with the true walls, may, when 
