Laccolith
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A laccolith is a body of intrusive rock with a dome-shaped upper surface and a level base, fed by a conduit from below. A laccolith forms when magma rising through the Earth's crust begins to spread out horizontally, prying apart the host rock strata. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith its dome-like form.
Idealized laccolith shape
Dolerite intrusion laccolith in Sydney, Australia
Laccolith exposed by erosion of overlying strata in Montana
Pink monzonite laccolith intrudes within the grey Cambrian and Ordovician strata near Notch Peak, Utah
Intrusive rock
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Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form intrusions, such as batholiths, dikes, sills, laccoliths, and volcanic necks.
Devils Tower, United States, an igneous intrusion exposed when the surrounding softer rock eroded away
An intrusion (pink Notch Peak monzonite) inter-fingers (partly as a dike) with highly metamorphosed black-and-white-striped host rock (Cambrian carbonate rocks) near Notch Peak, House Range, Utah, United States
Dark dikes intruded into the country rock, Baranof Island, Alaska, United States