The formation of `tors` on small rocky hills is associated with granite. A tor is a large, exposed outcrop of bedrock that is usually made of granite. Granite is an igneous rock that is formed deep within the Earth`s crust and consists mainly of quartz, feldspar, and mica. It is known for its durability and resistance to weathering.

When granite is exposed to weathering and erosion processes over a long period of time, it undergoes a process of exfoliation, which causes layers of the rock to peel off. This exfoliation process is responsible for the formation of tors, which are characterized by their rounded and jagged appearance.

The other options listed in the question - limestone, alluvial, and dolomite - are different types of rocks or geological formations that are not directly associated with the formation of tors. Limestone is a sedimentary rock formed from the remains of marine organisms, alluvial refers to sediment deposited by running water, and dolomite is a mineral composed of calcium magnesium carbonate. None of these are typically associated with the formation of tors.

Therefore, the correct answer is option 1 - granite.