Man's physical universe

xanabras

MANY DIFFERENT KINDS OF ROCKS 179

is larger if the magma cools still more slowly. A distinguishing

characteristic of igneous rocks is their massive and uniform structure.

Fig. 56. An example of igneous rock. Close-up of Devil's Post Pile National

Monument on San Joaquin River, Sierra National Forest, California. (Courtesy

of the U. S. Forest Service.)

There are two forms of igneous rocks which are quite well known,

namely, granite and basalt. Granite is a mixture of the minerals (a

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