We do not know. No more do we know how it comes to pass that this thin band (often only a few inches thick) of dead creatures should stretch all the way from Dorsetshire to Norfolk, and, I believe, up through Lincolnshire. And what is stranger still, this same bone-earth bed crops out on the south side of the chalk at Farnham, and stretches along the foot of those downs, right into Kent, making the richest hop lands in England, through Surrey, and away to Tunbridge. So that it seems as if the bed lay under the chalk everywhere, if once we could get down to it. But how does it make the hop lands so rich? Because hops, like tobacco and vines, take more phosphorus out of the soil than any other plants which we grow in England; and it is the washings of this bone-earth bed which make the lower lands in Farnham so unusually rich, that in some of them--the garden, for instance, under the Bishop's castle--have grown hops without resting, I believe, for three hundred years. But who found out all this about the Coprolites? Ah--I will tell you; and show you how scientific men, whom ignorant people sometimes laugh at as dreamers, and mere pickers up of useless weeds and old stones, may do real service to their country and their countrymen, as I hope you will some day. There was a clergyman named Henslow, now with God, honoured by all scientific men, a kind friend and teacher of mine, loved by every little child in his parish. His calling was botany: but he knew something of geology. And some of these Coprolites were brought him as curiosities, because they had fossils in them. But he (so the tale goes) had the wit to see that they were not, like other fossils, carbonate of lime, but phosphate of lime--bone earth. Whereon he told the neighbouring farmers that they had a mine of wealth opened to them, if they would but use them for manure. And after a while he was listened to. Then others began to find them in the Eastern counties; and then another man, as learned and wise as he was good and noble--John Paine of Farnham, also now with God--found them on his own estate, and made much use and much money of them: and now tens of thousands of pounds' worth of valuable manure are made out of them every year, in Cambridgeshire and Bedfordshire, by digging them out of land which was till lately only used for common farmers' crops. But how do they turn Coprolites into manure? I used to see them in the railway trucks at Cambridge, and they were all like what I have at home--hard pebbles. They grind them first in a mill. Then they mix them with sulphuric acid and water, and that melts them down, and parts them into two things. One is sulphate of lime (gypsum, as it is commonly called), and which will not dissolve in water, and is of little use. But the other is what is called superphosphate of lime, which will dissolve in water; so that the roots of the plants can suck it up: and that is one of the richest of manures.