Ecology of Humic Substances in Freshwaters Book

This is one of Darwin's more obscure works, and as such I think it gives a special measure of the man's calibre as a scientist and observer. On the one hand, it is all of a piece with his Lyellian gradualism to show what lowly earthworms can achieve across millennia of small-scale vomiting. On the other hand, it shows Darwin's thoroughness and mastery of method in even the lowliest of details, drawing on accounts of giant earthworms from foreign explorers, observations of leaf consumption in pots of earth, measurements of deposits over tombstones, the folk knowledge of farmers and the observations of archaeologists.

Darwin establishes how worms contribute to the creation of humus-rich soil, how they use gizzard-stones to grind vegetable matter, how they can survive months of inundation, how they produce terracing on pasture and how they manage to move megatonnes of soil downwards and out to sea from river basins. He establishes, fittingly given his most famous work, how small causes add up to geological effects. He shows how rocks descend into fields, how burial mounds are reshaped, how earth piles against the largest boulders and how traces of buried walls remain discernible in fields, an important consideration for archaeologists. How many of us would have presumed that worms are so interesting?

Another small masterpiece from one of science's largest figures, and eminently readable and engaging into the bargain.