The State Records NSW online passenger lists reveal he came from Postwick [pron. possick], Norfolk.
GENUKI (UK & Ireland Genealogy) has a charming description of the place from William White's History, Gazetteer and Directory of Norfolk, 1845.
In summary it says that Postwick, a parish of 241 souls, sits in a romantic glen which opens to the vale of the [River] Yare, near Yarmouth, and that most of the soil is owned by the Earl of Rosebery [Lord of the Manor].
The village is located 4 miles east of Norwich.
Some local residents of Postwick are listed in this directory, but no Clarkes.
Cantley, Norfolk is where Robert's wife, Elizabeth's father, Samuel Smith, came from.
According to the above source, Cantley is also near the River Yare.
It has a population of 210 souls and the Lord of the Manor is William Alexander Gilbert, Esq.
The village is 10 miles east of Norwich and 9 miles west of Great Yarmouth.
Among the local residents listed in the 1845 directory is a Mary Smith, shopkeeper.
The compiler of this information on GENUKI is Pat Newby.