Fig. 244. Section of Electric Peak. E. and Gray Peak, G,
Yellowstone National Park
Intrusive sheets and masses of igneous rock are drawn in black
The latter is the case: for the overlying stratum is intensely baked along the zone of contact. At the west edge of the sheet is found the dike in which the lava rose to force its way far and wide between the strata.
Electric Peak, one of the prominent mountains of the Yellowstone National Park, is carved out of a mass of strata into which many sheets of molten rock have been intruded. The western summit consists of such a sheet several hundred feet thick. Studying the section of [Figure 244], what inference do you draw as to the source of these intrusive sheets?
Fig. 245. Stone Mountain, Georgia, a Granite Boss