Southern Archaeology archaeologist Peter Petchey, who is directing the dig on the site, said yesterday it was exciting to find such early evidence of European settlement "right in the middle of town".
He described the find as "almost a bridge".
Logs covered with branches had been used to cover a small dip which could have been a stream, and extended further to protect against the extremely boggy conditions which prevailed in the 1800s in the area.
Early Dunedin was sometimes referred to as "Mudedin", he said.
He and his fellow archaeologists were getting first-hand experience of the wet, sticky mud.
It was difficult to say exactly how old the basic causeway was, but it could be as early as the late 1840s.
It had been made from local timber cut with metal axes, rather than stone axes, but timber samples would need to be taken to establish what wood was used.
The team of four archaeologists had almost completed exposing the causeway yesterday.
The site would be photographed and drawn.
Some of the logs would be lifted to see if anything of interest was underneath.
What would happen to the find was yet to be discussed with the DCC.
