A tunnel in liquid tar?

In a few spans it becomes soft and beyond that it's liquid tar for a league' 'How did they tunnel it?

"Help yourself, but don't expect anything like that liquid tar that you brew!"

Then the floor of the chamber cracked open, and a darkness like liquid tar flowed up around the feet of Blade's chair.

Workers apply black mastic - basically, liquid tar - to the exposed foundation.

Now each step downward seemed to take place against the resistance of liquid tar.

Its eyes looked like drops of liquid tar.

In some places one can put a stick through the asphalt and remove liquid tar.

The barrels oozed black drops of something that looked and smelled like liquid tar.

Or he may paint with liquid tar on thick squares of yellowed foam rubber nailed to the wall in a big grid.