[1] His father, after beginning life as a gardener, became a well-known local naturalist, who, in conjunction with William Bean, first explored the rich fossiliferous beds of the Yorkshire coast.

[3] When Owen's College at Manchester was founded in 1851 he became professor of natural history there, with the duty of teaching geology, zoology and botany.

[4] Williamson when little more than sixteen he published a paper on the rare birds of Yorkshire, in 1834 a monograph on the Gristhorpe Man, and still in 1834, presented to the Geological Society of London his first memoir on the Mesozoic fossils of his native district.

In geology, his early work on the zones of distribution of Mesozoic fossils (begun in 1834), and on the part played by microscopic organisms in the formation of marine deposits (1845), was pioneering.

In zoology, his investigations of the development of the teeth and bones of fishes (1842–1851), and on recent Foraminifera, a group on which he wrote a monograph for the Ray Society in 1857, were valuable.