Answer:
I dig out tiny caves and store gold and silver in them. I also build bridges of silver and make crowns of gold. They are the smallest you could imagine. Sooner or later everybody needs my help. Yet many people are afraid to let me help them.
I'm tall in the morning and short in the noon. I disappear at night but I will be back soon.
Without a bridle, or a saddle, across a thing I ride a-straddle. And those I ride, by help of me, though almost blind, are made to see.
A hill full, a hole full, yet you cannot catch a bowl full.
In we go, out we go. All around and in a row. Always, always steady flow. When we'll stop, you'll never known. In we go, out we go.
What covers its face with its hands, speaks no language, yet most known what it's saying?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?