In ch.47, after Mrs. Gardiner says that there is no absolute proof that Lydia and Wickham haven't gone to Scotland, Elizabeth answers:
"Oh! but their removing from the chaise into an hackney coach is such a presumption! And, besides, no traces of them were to be found on the Barnet road."
How could Elizabeth tell just from the fact that they switched from a chaise to a hackney coach, that they hadn't gone to Scotland? Also, I assume the Barnet road was a major thoroughfare leading from London to Scotland?