On Concretionary Patches and Fragments of other Rocks contained in Granite

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Abstract
No one who is in the habit of visiting granite-quarries, or who has had frequent opportunities of examining granite, either in a dressed or in a polished state, can have failed to observe that it frequently contains patches which resemble imbedded fragments of older rock. These patches or nests are usually, although not always, darker in colour than the granites in which they occur, while their form may be either rounded or more or less angular. In the first case the patch resembles an enclosed pebble, while in the second it often presents the appearance of a fragment of slate or mica-schist. Such patches most frequently have their outlines clearly and sharply defined, but they occasionally merge by almost insensible gradations into the enclosing granite. They are usually finer in grain than the granites in which they are found, and, from being less easily attacked by atmospheric agencies, not uncommonly stand out in considerable relief from the surfaces of weather-worn boulders. The union of the enclosed patch with the enclosing rock is generally complete, and their cohesion is so perfect that it is seldom difficult to obtain hand specimens exhibiting the line of junction of the two. Such bodies sometimes enclose crystals of felspar similar in all respects to those of the enclosing granite, excepting that in the majority of cases their angles are more distinctly rounded; patches of this kind occasionally contain others either of a lighter or of a darker colour than themselves. The inclusions in granitic rocks,

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