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| Figure 25. Contact between the Millboro Shale and the dike portion of the Sugar Grove basalt sill-dike at Stop 7. Basalt intruded along a joint (dashed line). Notice that a second joint set intersects the first at a 30° angle. Also notice the 0.25- to 0.5-m (0.8–1.6-ft)-diameter xenoliths of Millboro Shale in the basalt and the apparent flow foliation in the basalt. |