Many topographies are formed by magma beneath the earth’s surface i.e. the internal part of earth. All these rocks are called Hypabyssal Rocks.
A brief description of these rocks is as follows:
1. Batholith: These are also known as depth rocks. These are igneous rocks extending to a long distance and are hundreds of kilo meters long and irregular. These rocks are domeshaped. Their edges are like standing slope and base in deep depth. Their upper part is extremely irregular. At the time of formation of folded mountains, pieces obtained from fragmentation of rocks are helpful in their formation.
2. Lacolith: This is also known as mushroom rock or kukuchail. This word is made from the Greek word ‘Lekosh’, whose meaning is – water reservoir. It is formed of magma, large in size and is in the form of convex slope. Its shape is generally arcuate and base is flat. It is formed only in the sedimentary rocks.
3. Phacolith: It is also called masoor rock. It is a typically lens – shaped large rock. It is formed when magma solidified in the syncline of folded mountains at the time of volcanic eruption.
4. Lapolith: It is a vast form of the magma. When a shallow basin of concave – shaped is formed beneath the earth’s surface, then the accumulation which is formed in the shape of a saucer is called Lapolith.
5. Sills: It is also known as ralapatta. It is formed in the internal part of the earth, when the magma cools down and solidifies in the cracks of pre – formed rocks in a straight line. This layer of magma in the form of sills solidifies in parallel formations.
6. Dykes: It is also known as ral bhitti. When magma solidifies in the vertical form in the cracks of rocks, then this is called Dykes. Dykes can range from a few centi – meters to hundreds of meters. Dykes are generally hard.
7. Sheet: When magma accumulates horizontally in the cracks of rocks in an elongated and thin form, then it is called sheet. These topographies found in the internal part of earth are being presented with the help of the following fig.
