Factual error: It is barely credible that a young Victorian woman like Elena would even think about wearing a goatskin miniskirt - exposing her legs in those days would be akin to walking about topless nowadays. Even if she did those bright yellow cotton knickers - gleefully visible in the scene in the beehive - are in no way from the 1860s. Her pants are a hundred years ahead of their time.
Factual error: Miller rigs his booby trap by attaching the wires from the bomb to a pole down which a metal runner slides, so that when the runner touches the wires it completes the circuit and detonates the bomb. The trouble is, the pole is made of steel, and steel is very conductive indeed. Miller attaches the exposed end of the wire to the pole without any insulation or gap. The circuit will actually be completed when Miller attaches the battery, and he and his booby trap will be blown sky high.
Factual error: The rifles that Jake Cutter has Paul Regret dig up are Henry repeaters, or possibly 1866 Winchesters. Either way weapons unavailable in the period depicted in the movie.
Factual error: With the radiation belt on fire, the icecaps begin to melt. The Seaview is bombarded by huge chucks of ice. The ice is sinking to the bottom like stones. Ice floats, it doesn't sink.
Factual error: At the conclusion, the island gets blown apart by a volcanic eruption while the children and the hospital staff watch from aboard a schooner off the coast. A volcanic explosion of this magnitude would have created pyroclastic surges that would overtake the boat, killing everyone aboard. (During the 1883 eruption of Krakatoa a pyroclastic surge stretched 30 miles to the coast of Sumatra, killing residents of some villages along that coast before the explosion that triggered the devastating tsunami (which killed over 30,000 people).