Corrected entry: During the final train sequence, how does that gauge in the Delorean measure the pressure inside the train, when nothing is physically attached between it and the Delorean to measure that?
Corrected entry: As per http://www.bartleby.com/65/in/intern-co.html, J. J. É. Lenoir built the first gasoline powered internal combustion in 1859. De Rochas patented a design in 1862, and Otto built an engine in 1878. Gottlieb Daimler built what is considered the ancestor of today's internal combustion Engine in 1885. All this is by way of saying that gasoline would not have been impossible to find in 1885...especially considering that Edmund Drake drilled America's first oil well in 1859.
Corrected entry: In 1885 Marty meets his great-great-grandparents. His great-great-grandfather looks like him so that we can be sure of their relation. BUT, his great-great-grandmother looks like his own mother. This makes no sense as in this way his parents are related by blood due to the resemblance of their ancestors.
Corrected entry: There really should have been no reason for Marty to risk going back to 1885 to rescue Doc. Obviously, 1985 Doc being killed by Tannen, did not negate his eventual existence (as evidenced by 1955 Doc still existing). It's understandable Marty would want to prevent his friend being murdered, but when they learned of this fact in 1955, this event had already happened 70 years ago. 1955 Doc surely would have realized the pointlessness of Marty going to rescue his future self in the past when 1955 Doc would eventually become 1985 Doc again through the natural course of time. In light of this, surely 1955 Doc would have explained to Marty there was no reason to go back and possible cause more damage to the Space-Time Continuum.
Corrected entry: At the very end of the movie when Marty and Jennifer are at the wreck on the train tracks, the thing starts dinging and the arms lower, indicating that a train is coming. But if Doc is coming from somewhere else in time, then it wouldn't say a train was coming, and one dosn't come later.