Doctor Dolittle in the Moon by Hugh Lofting

Into this new heath and hill country we traveled for miles. And presently we arrived upon a rather curious thing. It was a sort of basin high up and enclosed by hills or knolls. The strange part of it was that here there were not only more tracks of the Giant Man, just as we had seen lower down, but there were also unmistakable signs of _fire_. In an enormous hollow ashes lay among the sands. The Doctor was very interested in those ashes. He took some and added chemicals to them and tested them in many ways. He confessed himself at last entirely puzzled by their nature. But he said he nevertheless felt quite sure we had stumbled on the scene of the smoke signaling we had seen from Puddleby. Curiously long ago, it seemed, that time when Too-Too, the owl, had insisted he saw smoke burst from the side of the Moon. That was when the giant moth lay helpless in our garden. And yet-how long was it? Only a few days!

"It was from here, Stubbins," said the Doctor, "that the signals we saw from the Earth were given out, I feel certain. This place, as you see, is miles and miles across. But what was used to make an explosion as large as the one we saw from my house I have no idea."