 Although layers are usually associated with sedimentary rock, the igneous rock of the butte is made up of very distinct layers. Evidently, the magma filled the laccolith in "pulses" with each new pulse forming another layer. 
Closer examination reveals a thin
lighter-colored layer between each of the
thicker, darker layers. This separation within
each pulse may have happened as a result of
differences in the densities and/or freezing
points of various minerals in the magma.
Another theory is that the thin light-colored
layers formed as a result of water soaking in
from the sandstone above before the next
layer of magma was
injected. |
1. David W. Baker Ph.D., Consulting Geologist & Technophysicist: Little Belt Consulting Services, Monarch, MT
2. Alt, David. "Charlie Russell's Square Butte" Profiles of Montana Geology; published by the Montana Bureau of Mines and Geology in cooperation with the Montana Magazine 1984
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11. The rock contains crystals. |
Below: This photo was taken in the same
general area as the two photos above. Having
a person in the photo
provides a sense of scale so you can realize
how thick the layers are. 
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