Forth Rail Bridge Blip in My Day

So on the train home from Inverness, I got muddled with my changes and found myself crossing the Forth Rail Bridge - when I should have got off at Perth.
Still, every cloud and all that...
I've never crossed the Forth by train before so I was all eyes.
Underneath the vivid red paint of the bridge, this rocky outcrop loomed.
It's called Inch Gavrvie and was home to a medieval fort/prison.

In 1882-4, Frances Groome's Ordnance Gazetteer of Scotland described Inch Garvie like this:

Inchgarvie, a rocky islet of Inverkeithing parish, Fife, in the Firth of Forth, 3 furlongs SSE of the North Queensferry coastguard station and 4 ½ NE of Long Craig near South Queensferry. Measuring 5 furlongs in circumference, it was crowned with a fort in the reign of James IV., which served as a state prison from 1519 till the purchase of the Bass in 1671, and which was visited in 1651 by Charles II. Inchgarvie was refortified and provided with four iron 24-pounders in 1779, after the alarm occasioned by the appearance of Paul Jones' squadron in the Firth; and it now forms the central support of the two great spans of the Forth Railway Bridge.—Ord. Sur., sh. 32, 1857.