Transform 1860s Australian (English?) map coordinates to modern ones

What is the coordinate system of Australia?

GDA is the current national standard, as applied through both geographic and projected coordinate systems. It replaces the AGD. In Australia, the standard projection used with projected coordinate systems is the Map Grid of Australia (MGA94) which utilises the Geocentric Datum of Australia (GDA).

How do you read GPS coordinates in Australia?

The numbers on the vertical lines increase in magnitude as you read left to right (towards the east). These lines are called eastings. The horizontal lines increase in magnitude as you read bottom to top (towards the north). These lines are called northings.
 

How do you convert XY coordinates to latitude and longitude?

Calculate latitude and longitude using the formula: latitude = asin (z/R) and longitude = atan2 (y,x). In this formula, we have the values of x, y, z and R from step 2. Asin is arc sin, which is a mathematical function, and atan2 is a variation of the arc tangent function. The symbol * stands for multiplication.