In 1846, he proposed that the distributions of montane plants and animals had been compressed downslope, and some oceanic islands connected to the mainland, during the recent ice age.

[2] This mechanism, which was the first natural explanation to explain the distributions of the same species on now-isolated islands and mountain tops, was discovered independently by Charles Darwin, who credited Forbes with the idea.

The British Association funded his studies based on dredging in the Irish Sea for biological specimens.

[5] In 1836, Forbes abandoned his medical studies and moved to Paris, where he attended the lectures at the Jardin des Plantes on natural history, comparative anatomy, geology and mineralogy.

[5] In April 1837, Forbes traveled to Algiers to gather material for a paper on land and freshwater Mollusca.

[4] In 1838, Forbes published his first volume, Malacologia Monensis, a synopsis of the mollusk species native to the Isle of Man.

[5] In 1838, Forbes presented a paper to the British Association at Newcastle on the distribution of terrestrial Pulmonata in Europe.

In the report, he discussed the influence of climate and of the nature and depth of the sea bottom upon marine life.

[5] Trilobite leading authority John William Salter was appointed on the staff of the Geological Survey and worked under Edward Forbes until 1854.

Salter replaced Forbes as palaeontologist to the survey and gave his chief attention to the Palaeozoic fossils, spending much time in Wales and the border counties.

During his later years, Forbes found more time in between lecturing and writing to order his stores of biological information.

In the summer of 1854, Forbes lectured at Edinburgh and in September served as president of the geological section at the Liverpool meeting of the British Science Association.

Forbes's widow married Major Yelverton in 1858 and forbade Geikie to work on the memoirs, seeking back all the papers.

In 1860, it was found that Yelverton had earlier married Maria Teresa Longworth and the separation had not been made with a witness.

Yelverton was accused of bigamy and Teresa Longworth wrote about her plight in a book Martyrs to Circumstance.

Geikie however had to exercise considerable diplomacy while writing the biography as Forbes had claimed that he had been sufficiently remunerated by the School of Mines.