Darwin and the Earthworm

I've been busy writing an article on earthworms for a magazine called 'Plant Life' that is published
twice each year by the Grotek people who produce organic fertilizers.
As always, some material just doesn't fit even though, to me it's interesting and valuable. So here
is what didn't appear in the article.
"Charles Darwin, having finished his major work on the origin of the species, turned his attention
to earthworms. He noticed how, in England, whole Roman pavements had disappeared beneath the earth.
'How can this be?' he thought. He observed (something he could do remarkably well) and realized that
the action of many earthworms over many years had buried these large sections of tile flooring. He
went on to argue that the great civilizations of history were based on the work of earthworms and
couldn’t have developed and flourished without them. Take the Nile delta, he said, home of
the Egyptian civilization. Earthworms throw up thousands of tons of castings, contributing the
fertility of the region, which allowed its wealth to accumulate and to be the basis of one
of the world's greatest cultures. It was the basis of their study of mathematics and their
 construction of the pyramids.
Sound like a tall story? Earthworms in the Nile delta can deposit up to one thousand tons
of castings per acre."
Read Amy Stewart's book "The Earth Moved: On the Remarkable Achievements of Earthworms". It's
well researched, very readable and quite gobsmacking.