X: The Unknown Reviews
It's better than you think.
A half decent British 50's sci-fi B-movie that would struggle to frighten even a 5 year-old (more likely bore them). Having said that it is entertaining enough to be worth a look and there is not exactly a huge number of killer radioactive mud movies out there so this is possibly the best of it's type.
The creeping gob from the center of the Earth doesn't show up until later in the movie but near the end it slithers around quite a bit which makes the whole endeavor more fun overall. This has to score some points for originality and for the subdued performance of Dean Jagger as Dr. Royston. There's an overabundance of silly science and clicking Gieger counters and the disposal of the monster is a yawner but there's some slightly suspenseful moments that make the whole thing worth a watch.