50 
GEOLOGY OF THE SECOND DISTRICT. 
In diagram No, 12, there is an attempt to illustrate a more diffused condition of the foreign mat¬ 
ters. Crystallization appears not to have influenced the form of the foreign matters at all. We 
find, judging from the appearances produced by weathering, that the separation has taken place 
by the molecular attraction, or by segregation. Those hard flinty places are readily discovered 
upon the weathered surfaces of the rock, but scarcely appear where the rock has been recently 
broken. Both the fine and coarse rocks contain siliceous masses, which are quite injurious, 
for lime, for marble, or any of the purposes for which limestone is so commonly employed. 
Although they are not seen without more than ordinary attention, yet it is not difficult to detect 
them by their hardness. Hence, when this limestone is quamed for making lime, it is neces¬ 
sary to examine the masses, and reject all those which are found hard, strike fire-with steel, 
or are difficult to break; for all such pieces are incapable of being converted into pure lime. 
The phenomena which it has been my object to illustrate, have been thus far drawn from 
limestone when associated with granite, or with a rock confessedly unstratified. If the subject 
of its origin were left here, there would remain still the question, whether those appearances 
which indicate its igneous origin were not due to its association with granite, and whether the 
non-appearance of planes of stratification is not the effect of tire granite upon it ? I have, 
therefore, examined this rock with great care, wherever I have found it associated with the 
schistose rocks, as gneiss and hornblende, or sienite. 
Most of the following diagrams are selected from those localities where gneiss takes the 
place of granite ; and it is proper to observe, that all which have been given, have been taken 
with care and fidelity. It has not been my object to select only those which favored my own 
views of the origin of this rock. I have, however, this to say, that I have seen none which 
were equivocal in their meaning, or which at all favored the metamorphic theory. 
The diagram in the margin shows the position of a mass of 
limestone in gneiss, near Whitehall in Washington county. It is 
analogous to what has already been exhibited in the preceding 
figures, when the same rock is associated with granite. 
This .may be taken in connection with the succeeding No. 14, 
a. Limestone, b. Gneiss. 
