During the 1800's Australia and Americian had a lot of cross migration, besides sailors and whalers jumping ship.

Before the Califorian Gold Rushes there were a lot of Australian Convicts that had escaped or migrated to the West coast of Americian, then During the Califorian Gold rush many Free Settlers from Australia joined in the rush.

When Australia Gold rush started many from the Califorian gold fields followed the gold and came to Australian Gold fields, then when the gold rush in Australia settled down many moved back to Americia for the Alaskian and Yukon gold rushes and many returned for the Kalgoorlie and Palmer gold rushes

Google "Thomas Francis Meagher".

Irish Nationalist, convicted of sedition, transported for life. Escaped, made it to America, ended up a Brigadier General in the Union Army in the Civil War, then acting Governor of Montana Territory. All before drowning in the Missouri at age 43...

Peter