The message is the medium of The Control of Nature
. In a series of three essays, each regarding a different geographical region, McPhee shows that in the war between man and nature it's a case of the humans on horseback facing a blitzkrieg of geological heavy artillery. What amazes McPhee, and thus what comes across to the reader, is the arrogant hubris of the people who feel that nature can be controlled. One essay is about the Mississippi river, and how it has been channeled by dikes and levees to stay on the course that it has been set on since the early part of this century, although anyone can see that it is in its nature to change course. Essay two is about the lava flows in Iceland, where the engineers used the cooling power of the sea to divert the flow from a township--at least for now. And, last, McPhee covers the shifting mountainsides of southern California--not the mud of the beach homes, but the Santa Gabriel mountains which are so geologically new that the rocks that they consist of are more akin to sand. In each essay, the humans have fought the battle to a draw, but the enemy is worse than any evil fantasy. Nature is unsleeping, its forces are legion, and each battle it suffers no losses. The expense, in both money and lives, of trying to withhold the inevitable seems to doom the humans to lose. But they do not give up.