Frightful Mortality.
--One of the most fatal explosions of yellow fever on record occurred about two months ago on the coast of Africa, and is described in the London Lancet of the 3d ult. In the Island of McCarthy, on the Gambia, the malady suddenly broke out without any traceable cause, and attacked all the inhabitants, not one of whom recovered, except Capt. Frazer, a naval officer, in command at the station.