Which pair of events describes a significant cause and effect that occurs in the story?

So we put the horses into as much of a trot as the deep snow would allow, and before long it was evident that we were gaining on our predecessors, for the tracks grew more distinct. We hurried along, and at the end of an hour the tracks looked still newer and fresher — but what surprised us was that the number of travelers in advance of us seemed to steadily increase. We wondered how so large a party came to be traveling at such a time and in such a solitude. Somebody suggested that it must be a company of soldiers from the fort, and so we accepted that solution and jogged along a little faster still, for they could not be far off now. But the tracks still multiplied, and we began to think the platoon of soldiers2 was miraculously expanding into a regiment3 — Ballou said they had already increased to five hundred! Presently he stopped his horse and said:

“Boys, these are our own tracks, and we’ve actually been circussing round and round in a circle for more than two hours, out here in this blind desert! By George this is perfectly hydraulic!”

[5]Then the old man waxed4 wroth5 and abusive. He called Ollendorff all manner of hard names — said he never saw such a lurid6 fool as he was, and ended with the peculiarly venomous opinion that he “did not know as much as a logarythm!”