Answer:
Lunar Maria-
'Maria' is a Latin word meaning "seas", and they are large, dark, balsaltic plains found on the surface of the moon. Astronomers believe they were originally formed by ancient volcanic eruptions. To the naked eye, they appear very dark, and this is due to iron-rich composition. They cover nearly 15% of the moons surface - most of which is on the near side to the Earth (the side we can see).
In fact, it is because of Lunar Maria that people often think they see a face in the moon.