The islands are artificial creations, originally having formed part of the Town Meadow. Immediately after the 1793 new cut by the Grand Junction Canal Company, a single island was formed, and sometime thereafter an overflow cut was made through that island to facilitate run-off in times of heavy rain. That is what still divides the two sections of what was briefly a single created island.
West of Dock Road was the copyhold of Dr Johnson, to the East belonged to George III as an osier bed. The canal company had to purchase land surplus to requirement under their Act, and arranged to sell back that surplus [both Johnson’s and GIII’s] to Johnson at a presumably marked down price – so Johnson ended up with GIII’s bit as well, no doubt at a nice profit!
Strictly speaking then, both west and east of MSO’s operation could be called ‘Johnson’s Island’
Tearing my hair out with photobucket’s new codes, trying to figure how they translate for this site, but if it works, this is the relevant conveyance [Earl of Cardigan acting as Trustee for GIII] –