Another great contribution from a periodicvideos viewer.
This one comes in response to an anecdote from The Professor.
In one of our videos about crude oil, The Prof casually mentioned a lake of oil in Trinidad.
Well, today I received an email from a viewer named Roy who has visited the so-called "Pitch Lake".
Roy said: "The professor mentioned Trinidad in the crude oil video. These two photos are from there - I hope he likes them.
"The lake is about 1 mile by 2 miles in size, and they have been taking (pitch) from this for years and it just keeps refilling."
Here are Roy's pictures:
And here's the video which prompted his email: