Grammar help for a 6-year-old: Correcting two 'Mountains' sentences (rock, pebbles, soil)

Here are your corrected sentences and a short, simple explanation.

Original:

• Mountains are big bumps of ground built from hard rock, pebbles, and soil.
• Mountains are tall, rocky waves made from hard rock, stones and soil.

Corrected:

• Mountains are big bumps of ground made of hard rock, pebbles, and soil.
• Mountains are tall, rocky waves made of hard rock, stones, and soil.

Short, simple sentence you can use:

Mountains are tall, rocky bumps made of hard rock, stones, and soil.

Why I changed them (easy words):

1. I used made of because that is the usual way to say what something is made from.
2. I added a comma before and in the list to make the list clearer (stones, and soil).
3. I made the words match so the sentences sound the same and are easier to read.