> Graph theory, a branch of topology, and spherical geometry > (displaced by Newtonian calculus in recent memory)
I don't think that spherical *geometry* (or any other non-Euclidean geometry) was ever particularly important as a high school topic. If you meant spherical *trigonometry*, that's a horse of another color.
And your suggestion that it was displaced by Newtonian calculus is arguable, at the very least. Spherical trig may just have died on the vine when it was no longer expected that high school graduates could become surveyors and/or navigators with no further formal education. In education, such deaths are usually quite protracted, and that explains the "recent memory" part.
- --Lou Talman Department of Mathematical & Computer Sciences Metropolitan State College of Denver