Surrounded by water on three sides, much of the peninsula foreshore was man-made in the late 1800s.

And, according to the late Stockton maritime historian Terry Callen, where you walk on the "Ballast Ground" on the suburb's western shore, by the Hunter River, you are treading on foreign soil.

No one knows exactly how much ship ballast was dumped, but the looming anniversary of the 1906 San Francisco earthquake on April 18 gives a clue as to the variety of rubble involved.

In the dying days of the sailing ship era, the port of Newcastle was one of the last refuges of the graceful, but doomed, windjammers. To compete in the new age of steam, they relied on hauling bulk cargoes, such as grain or coal, around the globe to survive.

From Newcastle, they took coal cargoes across the wide blue Pacific to America and also to South America, to ports with exotic names like Valparaiso and Iquique in distant Chile.

From around 1900, the coal trade was left almost exclusively to sail vessels.

Overseas demand was huge. After a coal strike ended in 1896, more than 100 windjammers packed Newcastle Harbour. Some of them waited for months.

But coal loading was a very slow, laborious process. One famous historic picture even shows seven waiting ships abreast at the Stockton ballast jetties in October 1900.

Another photograph shows the same western shore with 19 windjammers in a long line packed two abreast awaiting coal in 1912.

Sail vessels arriving in port wanting a coal cargo first had to tie up, then tip out about half of their ballast - rocks or other heavy waste material needed for ship stability at sea - into shallow harbour water.

The vessel would then be towed across the Hunter River to North Carrington to load part of the coal cargo. Then it would return to the western Stockton foreshore to unload the rest of its ballast, before returning again to load up the remainder of its coal cargo and depart.

This led to all the land being gradually reclaimed down the western shore of Stockton peninsula, parallel to Fullerton Street.

The sail vessels moored from near Punt Road all the way up to Meredith Street, Stockton, an area so remote it was nicknamed "Siberia".

When enough stone ballast had been discharged from these wind ships to create a long, new shoreline going north, dredges came in, pumping silt behind this seawall until it reached the same height.

By 1914, just before the start of World War I, there were 18 ballast jetties along this shore.

Oddly enough, the windjammers were helping fuel the end of their world as they knew it by hauling nitrate cargoes (for fertilisers or explosives) from South America to Germany, before securing fresh cargoes or coming back only in ballast to Newcastle for more coal.

More ships came in ballast here than "the rest of Australia put together", according to the Newcastle Chamber of Commerce in 1899.

But decades before this major coal rush, almost 1000 tons of ballast was arriving here every week in ships.

Maritime historian Terry Callen once wrote that in 1907 about two million tons of ballast arrived in NSW, the bulk of it to Newcastle - to stay forever.

What exactly did the ballast shipped here from all over the world contain? It was a mixed lot, as reported in the 1870s. There were shiny black stones from Mauritius in the Indian Ocean, rock mounds from Scandinavia, bluestone from Melbourne, green trap from New Zealand, plus soil from Peru, Chile and Ecuador, damaged green roof tiles from China, layers of London flint, limestone from Singapore and stones from the sunny Mediterranean.

The most interesting source of ballast, however, was from the horrific San Francisco earthquake and the four-day fire that followed in April 1906.

Initial reports said only 500 people were killed, although the death toll is now estimated at more than 3000 people with 200,000 residents left homeless. More than 80 per cent of "Frisco" was destroyed. It was one of the deadliest earthquakes in US history, causing an estimated $US11.4 billion damage.

Once the smoke cleared, the city's rubble was given away free as ballast to sailing ships returning to Newcastle to load coal. In one month alone, 30 ships came here laden with ballast from the earthquake-ravaged city.

And there were some surprises later. In the 1930s, the eroded riverbank revealed small bricks on the reclaimed land along with rusted bicycles, smashed typewriters, silver dollars, crockery, even an old cannon, or so it's said.

Six unbroken glass goblets in a box were also once discovered on the ballast ground having miraculously surviving the 1906 quake, the long sea voyage, and final dumping here.

Other exposed piles of deep red bricks are even speculated to have come from the then main street of San Francisco, the aptly named to Stockton Street, now the modern heart of Chinatown.

It's not the last time rubble has been successfully recycled. After Nazi bombs rained down on London in World War II, street rubble from the blitz was used as ballast in ships collecting Lend Lease supplies from America.

Some even found its way into the foundations of New York city streets.

But there's another secret buried in Stockton ballast. Historian Terry Callen always believed there was more Melbourne bluestone dumped on his suburb's foreshore than there ever was overseas ballast.

Newcastle coal was once desperately needed to fuel the Melbourne gasworks. He may be right, as it's used in many spots if you care to look inner-city Newcastle.

Another example is at today's wave trap near the port entrance. The small breakwall here was built mainly of Melbourne bluestone dumped by coasters at a specific ballast wharf.

(Pre-1880, there were at least 30 small, sailing colliers from Victoria regularly coming here. The biggest, the 724-ton wooden barque Result, always carried 350 tons of bluestone ballast in her bottom).

The dark, extremely durable slate bluestone was also often dug up, sold and used in inner-city paths, roads and walls. A prime example is at the western end of Church Street, The Hill. Here, in tiny McCormack Street, sandstone in the large side wall of the old Woodlands mansion has been topped off with bluestone.

But the final irony is that ship ballast wasn't always welcomed to be dumped in Newcastle Harbour. In the 1850s, ship masters were fined for indiscriminately discharging ballast into the harbour.

A fear of plague from rats and disposal of ballast from "infected ports" remained a problem for 50 years.

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