X the Unknown (1956)

Description[from Freebase]

X the Unknown is a British science-fiction / horror film made by the Hammer Films company and released in 1956. The film takes place in the Lochmouth area of Scotland, near Glasgow. A group of soldiers are taking turns using a Geiger counter to find a small and harmless hidden source of radioactivity in a wide pit area. Private Lansing finds another mysterious source of radiation where ground water starts to boil. As the other soldiers begin to run, there is an explosion. Lansing, who was closest to the explosion, dies of radiation burns while another soldier has bad radiation burns to his back. At the site of the explosion, there is a Y-shaped crack in the ground with no apparent bottom. Dr. Royston from a nearby Atomic Energy establishment at Lochmouth is called in to investigate, along with Inspector McGill who runs security at the UK Atomic Energy Commission. That night, a local boy, on a dare from his friend, goes to a tower on the marshes. He sees a horrific off-camera sight. He refuses to tell his friend what has happened but continues running. The friend follows.

Portions from Freebase, licensed under CC-BY and Wikipedia licensed under the GFDL