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see the diorite sill above us. We will walk up and be level with it as you can see ahead.
It is about about 100 feet thick, and thus can be used as a very accurate scale for determining the height of mountains on which it is discernible.
This imposing layer of rock, unlike the lava, never reached the surface in a molten state, but was intruded between beds of sedimentary rook and thus became a sill instead of a flow. We need only a glance to determine its intrusive nature. Wherever it occurs it is bordered at top and bottom by thinner gray layers. These are Siyeh limestone which was changed to marble by the tremendous heat of the diorite during its intrusion. This effect is termed contact metamorphism by geologists. Because this contact-metamorphosed zone is at both top and bottom of the sill we know the latter was intruded into the adjacent rocks. Lava flows, even though covered later by sediments, of course alter only the underlying rocks.
It is about about 100 feet thick, and thus can be used as a very accurate scale for determining the height of mountains on which it is discernible.
This imposing layer of rock, unlike the lava, never reached the surface in a molten state, but was intruded between beds of sedimentary rook and thus became a sill instead of a flow. We need only a glance to determine its intrusive nature. Wherever it occurs it is bordered at top and bottom by thinner gray layers. These are Siyeh limestone which was changed to marble by the tremendous heat of the diorite during its intrusion. This effect is termed contact metamorphism by geologists. Because this contact-metamorphosed zone is at both top and bottom of the sill we know the latter was intruded into the adjacent rocks. Lava flows, even though covered later by sediments, of course alter only the underlying rocks.