We were struck by the enormous blocks of stone of which it is constructed.  They were all quarried from the Isle of Portland, which forms one side of the harbour, by convicts who are confined in a large stone prison at the top of the hill.  Both on the breakwater and on shore are strong stone forts for the defence of the harbour, in which, in time of war, would also be stationed some heavy ironclads; so that a large squadron alone would venture to annoy the shipping within.