142 
AMERICAN GEOLOGY. 
narrower vein is divided; but the quality of the ore and the 
thickness is quite different. Fig. 28. The wider vien is four- 
Fig. 28. teen feet thick, and the 
others six, three, and two 
feet. These are known as 
the Cook veins. Thev tra- 
•/ 
verse a north and south range. 
The rock is gneiss and the 
lamina of the planes nearly vertical. 
The experience which has been acquired in mining in north¬ 
ern New York, has now become valuable. The exploration of 
the magnetic ores was prosecuted at an early day, and in conse¬ 
quence of the adventurous spirit of the owners of mineral lands 
in this district, trial shafts were sunk at points which were not 
promising at the surface. The rock was observed to be charged 
with particles of ore which were found to be persistent and to 
have a direction correspondents th the veins which had been 
proved. On sinking however a shaft upon those stripes of rock 
and lean ore, it was found that the iron increased, and at a 
moderate depth, a productive vein of metal was established. 
A mine widely known as the Palmer vein, is a good example 
of the change from a very lean ore to a rich one. A vertical 
section of the mine, fig. 29, illustrates the fact under consider- 
Fig. 29. 
a Dykes, b Increased Ore, c Disseminated Ore, d Mass of Ore. 
