The diagram (in the picture) shows the geology of a cliff section that has been formed over different periods of time at varying temperatures.

a minor intrusion known as a sill is labeled b on the diagram. explain why the crystals in the sill, b, are smaller than those in the large intrusion labelled a.

Sill B has a lack of space.

Explanation:

Crystals form in cooling magma that will eventually form igneous rock. As the rock cools crystal minerals grow. Crystals in intrusive igneous rock will have more time to grow as it takes longer to cool than igneous rock forming on the surface. This is why we will find crystals in both A and B. However, in B the magma will have cool quicker and the crystals will have less time to expand. It will also have fewer options for space. This causes the crystals to be smaller here.