Slow Lightning - Steven Popkes

Ira and Gray found the egg on an abandoned ferryboat. It was wrinkled, with smears of red and yellow, and bigger than a basketball. They weren't sure why it was there, only that it must have been left there on purpose.

The next day, the egg had grown...

"Slow Lightning does a remarkable job of conveying the sheer strangeness of the universe and the future." -Poul Anderson