The Seashell on the Mountaintop: A Story of Science, Sainthood, and the Humble Genius who Discovered a New History of the Earth, by Alan Cutler. Dutton, 2003.
In Dr. Jay Wile's Exploring Creation With General Science, my seventh grader and I read about the principle of superposition, along with other basic geologic principles. It wasn't a hard concept to grasp: the older things are lower down in the ground than the newer things. We compared it to a hypothetical bedroom floor that hasn't been picked up in several years and that holds an accumulation of clutter and debris relating to the owner's life over that time period. Birthday cards from two years ago would be found somewhere below last week's dirty socks, and so on. The scientist who is honoured by having those principles named for him, is Nicolaus (or Nicolas) Steno (1638-1686). In the 1600's, names were somewhat fluid, and Steno started out with a Danish name, but it changed depending on where he was and who he was writing to.
When we think of creationism today, there are certain points that we assume that Christians taking the Bible either "literally," or at least seriously, believe. But in the seventeenth century, taking the Bible literally included ideas that even creationists today would find strange; for example, that extinction of any species was Biblically impossible, because that would mean that God wasn't taking perfect care of his Creation. Any suggestion that any part of creation could change over time, or at least since the time of Noah's flood, was viewed with disdain and suspicion. It was impossible to imagine that dry land, especially high places and mountains, could at one time have been seas, and that those seas had deposited sediment that had become rock, and that inside that rock were the fossilized remains of creatures that were sometimes familiar, sometimes not. God's world a) just wasn't old enough to have gone through that much change, and b) wasn't supposed to change anyway. Everything was where it had been put at Creation, or possibly where it had gotten dumped in a short period of time during the Flood. Anything that didn't fit those parameters...well, there were always explanations. Fossilized sharks' teeth, seashells far from the sea, even stones must have fallen from the sky, or maybe grew from the ground. After all, didn't farmers find a brand new crop of stones in their fields every spring?
And this is where Nicolaus Steno entered the story. He began as an anatomist, and quite a well known and skilled one; he discovered tear ducts and a few other important things about the human body. But a chance opportunity to dissect a very large shark's head forced him to notice the similarities between all those rows of teeth, and the petrified sharks' teeth that were popular for their "medicinal properties" but which were believed to be just tooth-shaped stones. He gradually abandoned his anatomical studies for geological ones...except that there really was no such thing as geology, until he invented it, or specifically, stratigraphy.
There is much more to his personal story, his travels, his writing, and his discoveries; and as the author says somewhat regretfully, this particular book could not spend as many pages as he would have liked discussing Steno as an anatomist, and Steno as a priest (he converted to Catholicism, became a priest and then a bishop, and was beatified in 1988). However, we do get quite a bit of those different sides of Steno's life, and I don't think most readers would find the story unbalanced.
I was a bit put off at first by a tone of "people used to believe this, but we don't mix religion with science now," but as the book went on it seemed that the author expressed more respect for Steno's strong religious beliefs. As Cutler points out at the end of the book, in the post-Galileo world it was often not the church that argued with new ideas in science, but other scientists--physicists, for example, who wanted everything to line up neatly and rationally. He makes this comment in the epilogue: "Until very recently, religious and scientific arguments were advanced by both sides in every important scientific controversy. Too often what filters down to us in the history books are the scientific arguments of the winners and the religious arguments of the losers. Thus the picture of a long-standing rift between the two."
Having finished Seashell, and chewing on some of Steno's observations that would seem to cause trouble for young-earth creationists today (perhaps more than they did in his own time?), I did a short Google search for Nicolaus Steno plus creationism. I was not surprised to find a Christian Science Monitor article referring to him as "the saint who undermined Creationism"; but I was very surprised to see a page praising him highly on the Creation Ministries International website. I think that is due to the fact that although Steno opened the doors to a new understanding of the earth's history, which eventually led to the more problematic doctrines of geologists like Lyell, he did not get specific about when all this might have happened. What was revolutionary enough in his time was simply saying, first this, then this.
The book isn't difficult to read, and I think it would be quite suitable for students in middle school and up. It offers such a good introduction to the state of European religion, science, and life in general in the late seventeenth century, that it would be an excellent addition to a study of that time period.