When I was in fourth grade, in the mid-1980s, my advanced reading class finished the regular textbook several weeks early, so our teacher selected a novel for us to read. I only saw the cover though, which featured a Kirby-boom-tube-like tunnel with a human figure inside it. The tunnel was probably a time travel device, since the terrain surrounding the visible end of the tube was filled with jungles and dinosaurs.
I never got to read the book, because a creationist parent complained, and the teacher selected a different, non-SF book for the class. Any idea what this was?