Why did the driver stop and go to the blue flames?

Question

In the novel Dracula, why did the driver of the carriage that was taking Jonathan Harker to Dracula's castle stop and go where the blue flames were?

Suddenly, away on our left, I saw a faint flickering blue flame. The driver saw it at the same moment; he at once checked the horses, and, jumping to the ground, disappeared into the darkness. I did not know what to do, the less as the howling of the wolves grew closer; but while I wondered the driver suddenly appeared again, and without a word took his seat, and we resumed our journey.

What was he doing there exactly?

Answer 1

In chapter 2, Dracula explains this behavior to Harker. It has to do with a local superstition. The locals believe that the blue flames indicate locations where treasure (gold) is buried, but that it's cursed:

[Harker] asked [Dracula] of some of the strange things of the preceding night, as for instance, why the coachman went to the places where he had seen the blue flames. He then explained to me that it was commonly believed that on a certain night of the year, last night, in fact, when all evil spirits are supposed to have unchecked sway, a blue flame is seen over any place where treasure has been concealed.

Most likely, the driver is either:

1. Planning to come back later and try to dig up the gold, so he needs to know where it is, or
2. Wants to know where the gold is buried so he can avoid accidentally being cursed by it.

Dracula implies #1, though also that it's a fools errand, later in the conversation:

Why, even the peasant that you tell me of who marked the place of the flame would not know where to look in daylight even for his own work.

Answer 2

Dracula spoke the truth to Harker that the blue flames revealed buried gold.

When Harker sneaked into Dracula's chamber in Chapter 4, he found gold coins, forged over various centuries, that looked as if they had been buried for years.

The coachman was a disguised Dracula. He marked those locations that night (since the opportunity only occurred once a year), and went back later to acquire the gold buried in those places.