Read the whole thing here. It is well worth your time.
This is the part I was looking for:
"On Dirty Jobs, I’m no expert, and I’m even less of one here. But I have a theory, and it goes like this – all jobs rely on one of two industries – mining and agriculture. Every tangible thing our society needs is either pulled from the ground, or grown from the ground. Without these fundamental industries there would be no jobs of any kind. There would be no economy. Civilization begins with miners and farmers, and polite society is only possible when skilled workers transform those raw materials into something useful or edible."