"I sat on the hill in a sort of despair. There was no town nearer than Chichester at which it was even remotely probable that there would be such a thing as an artist's colourman. And yet, without white, my absurd little pictures would be as pointless as the world would be if there were no good people in it. I stared stupidly round, racking my brain for expedients. Then I suddenly stood up and roared with laughter, again and again, so that the cows stared at me and called a committee. Imagine a man in the Sahara regretting that he had no sand for his hour-glass. Imagine a gentleman in mid-ocean wishing that he had brought some salt water with him for his chemical experiments. I was sitting on an immense warehouse of white chalk. The landscape was made entirely out of white chalk. White chalk was piled more miles until it met the sky. I stooped and broke a piece off the rock I sat on; it did not mark so well as the shop chalks do; but it gave the effect. And I stood there in a trance of pleasure, realising that this Southern England is not only a grand peninsula, and a tradition and a civilisation; it is something even more admirable. It is a piece of chalk." The Latest and the Greatest GKC
I am a physics professor, and it's true -- not all chalk is the same. Some chalk is absolute garbage -- Crayola chalk, for example. I'm surprised I have never heard of this, especially since I did a postdoc at the University of Tokyo years ago, back when we used transparencies instead of PowerPoint. I think that might have been the difference: a prepared presentation is different than a class, so I rarely if ever used chalk while I was there.