The cooled lava pools on the surface of a crater are called what

C. Maria Early scientists thought the dark stretches of the moon might be oceans, and so named such features mare, which is Latin for "seas" (maria when there are more than one). They are oceans of a sort, but rather than water, such bodies are made up of pools of hardened lava. Early in the moon's history, the interior was molten enough to produce volcanoes, though it quickly cooled and hardened.