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Igneous Rock Formation:
Igneous rocks form when molten rock, originating from deep within the earth, cools and solidifies. Igneous rocks can be intrusive or extrusive. Intrusive rocks (plutonic) form when magma cools beneath the surface of the earth. Extrusive rocks (volcanic) form above the earth’s surface in the form of lava flows. Intrusive rocks tend to be coarse grained, as the magma cools slower (being underground) giving sufficient time for large crystals to grow. Extrusive igneous rocks cool rapidly being above the earth’s surface, producing fine grained or glassy rocks. Basalt is an example of an extrusive rock whereas gabbro and granite are coarse grained having cooled slowly being deeper underground. Diabase, often called Dolerite, is a fine to medium grained, intrusive igneous (volcanic) rock. It is a typically shallow, extremely hard rock commonly quarried for use as monumental stone. Chemically and mineralogically, diabase closely resembles the volcanic rock basalt, but is somewhat coarser and may contain tachylite (dark mafic glass).
Batholiths, Dykes, Sills and Laccoliths:
A batholith (a major pluton) is an emplacement of igneous intrusive rock that forms deep in the Earth's crust. Minor plutons include dykes, sills and laccoliths, all of which are generally shallower. A dyke is an emplacement of igneous rock that crosses earlier geological layers, whereas a sill runs parallel to earlier geological strata. A laccolith is another type of intrusion that forces the rocks above to uplift and form a dome.
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). Most limestone is composed of skeletal fragments of marine organisms such as coral, forams and molluscs. It is generally light in color and makes up about 10% of the total volume of all sedimentary rocks worldwide. It is often used as a building material, as aggregate in roads, as pigment or filler in products such as toothpaste or paints and as a chemical feedstock for the production of lime.
The term 'fold' is used in geology to describe one or more, originally flat level surfaces (sedimentary strata), that have become bent or curved. This deformation is the result of endogenetic processes which means that it takes place within the Earth's crust and has not been acted upon by external forces. This 'folding' is likely to be some aspect of plate tectonics (pressure and high temperature). Folds vary in size from microscopic crinkles to mountain-sized entities. Large-scale folds are found primarily along collision boundaries between two tectonic plates.
Posted coordinates will take you to a small roadside pulloff on the East side of the highway. Site #1 can be seen from here. Site #2 can be seen by walking 450 feet south, staying outside of the guardrail (safe side, east side) on a small roadside trail. There is no need to cross the highway once parked. All questions can be answered after viewing the formations from these 2 sites. Actually all questions can be answered just by driving past and observing the 2 sites if you are quick. They are quite obvious. If you decide to do this as a drive-by just be wary of other drivers (which are few and far between normally) in the area.
1. Is the geologic formation found here a dike or a sill?
2. The overall thickness/width of the dike/sill is?
3. In your opinion, was this fold formed along a major collision boundary?
4. Is the fold found within an igneous, or a sedimentary rock type?
5. Of what rock type is the dike/sill composed of?
6. At which site do you find the fold?
Email your answers to the questions, to me, using the link in my profile only. If your answers are not received by me, your log will be deleted. Photos are accepted and appreciated as long as the answers are not pictured. You do not have to wait for confirmation from me before logging this cache as completed. Most of all……learn……and enjoy the view.
(No hints available.)