Information is very thin on the ground!
I went to Cork with my mum last Easter to do mor ancestry. Unfortunately didn't find much info about the Rock side of the family.
My g-g-grandfather was Archibald Rock married Margaret Palmer who is believed to come from St. Helena ( I have a photograph of her)They had daughter Margaret who married Edward Hassell in Cork city.
In 1870 Archibald Rock was mentioned in the Cork City directory as being 'shopkeeper' on French's Quay in Cork City- maybe suggestion of the French connection ???
In the BMD there was a mention of these Rocks:
Birth 1777 - Patrick
1828 - catherine
1867 - Thomas Charles
1851 - Patrick
1874 - George
I hope this may give you a lead, but its interesting anyway!