Trivia: During the subway crash scene, you can hear the Wilhelm scream.
Trivia: The first few disasters listed on the sheet are: Malpassat Dam, France (December 2nd 1959), Coalbrook Mine, South Africa (January 1st 1960), Agadir earthquake, Morocco (February 29th 1960), Valdivia earthquake, Chile (May 22nd 1960), asylum fire, Guatemala City (July 14th 1960) and Nedelin disaster, USSR (October 24th, 1960). Incidentally, Lucinda's listing of dates is inconsistent; sometimes she wrote them the American way (month before day), others day before month.
Answer: It is a rock from the ground of the final location on the list, where the spaceship has landed to transport Caleb and Abby to their new home. It is merely a clue as to where they should go on the day of October 19th.
Katie..x