The correct option is 1 and 3 only.
Explanation
Phacoliths are intrusive igneous rock bodies that form when magma solidifies within the Earth's crust, specifically adapting to the structure of folded rocks.
- Statement 1 is correct: Phacoliths are characterized as wavy masses of intrusive rocks. They typically occupy the crests of anticlines (upward folds) and the bottoms of synclines (downward folds) in folded strata. The magma fills these spaces, resulting in a shape that follows the undulations of the fold, appearing as a wavy mass.
- Statement 2 is incorrect: Phacoliths are associated with folded sedimentary strata, not horizontal bedding planes. Intrusions that solidify horizontally along the bedding planes of sedimentary rocks are generally known as sills. The formation of a phacolith is dependent on the structural spaces created during the folding process.
- Statement 3 is correct: These formations have a definite conduit or channel connecting them to a magma source beneath. The magma rises through this conduit (often resembling a dyke) to fill the cavities in the anticlines and synclines.
Key Takeaway: Phacoliths are lens-shaped intrusive landforms found in the crests of anticlines and troughs of synclines in folded regions, connected to a deep magma source via a conduit.