C.R. Martin button
Queensland Railways
11th Regiment of Foot (North Devonshire)

Backmark: C. Pitt & Co 50 St Martins Lane London Charles Pitt & Co operated from 50 Martins Lane from 1875-1895, so this is after the period in Australia of 1845-57.
For another example:
http://www.austbuttonhistory.com/uncategorized/20th-november-2020/
Woolworths
General Plastics must have liked this design, as they produced it in both sew-through and (with out the holes) shanked versions.

Shanked and pearlised versions.