144 
AMERICAN GEOLOGY. 
not examined with care be mistaken for the walls. An ex¬ 
amination will lead to the detection of their true form which is 
that of a wedge. It is scarcely necessary to add that they will 
disappear in the progress of mining. 
Fig. 31. 
Fig. 31, illustrates the fact I have just stated. It is a sec¬ 
tion of a part of the Hall vein, in Moriah, Essex county, the 
parallel masses of rock, are, d, quartz, a, ore; but they may 
consist of hornblende or feldspar. An interesting instance of 
the same kind, is now being exposed at the Old Sanford ore 
bed, where masses of trappean rock and feldspar, are intruded 
into the midst of the ore. Fig 32. In this instance the strike 
of the vein is not determined, and hence it is impossible to say 
whether these masses are parallel with the walls or not. Each 
of those masses might be regarded as limiting the ore, but on 
cutting through them, equally good ore is found in the spaces 
between the dykes, as at any other part of this remarkable 
vein. 
Since the foregoing was penned, I have ascertained, by an 
examination of the wall, that three of the dykes have disap¬ 
peared, and the three obliquely placed masses of rock are en¬ 
tirely removed, and there now appears a breast of solid ore 146 
feet long and twenty-five feet high, traversed by a single dyke 
