[4] Lying between Dumbarton and Dunglass Castle below Dumbuck Hill the island is recorded as 'Green Inch' on William Roy's map of 1747–55.

Although convenient as a means of crossing the river on foot and horseback, the shallowness of the estuary meant that larger ships could not reach Glasgow.

Jetties were built to encourage the water flow to scour the shoal, but again met with limited improvements in the channel's depth.

[11] However, Dumbuck Shoal remained a problem - "The first and grand obstacle is Dumbuck Ford (12 miles below Glasgow Bridge), where, the river dividing itself into two channels, the reflowing current is greatly weakened, and the bottom, being covered with a crust of hard gravel, cannot be worn down to the proper depth; but if a jetty were extended over the south channel, to confine the current, and the hard crust of gravel removed by dredging, the reflowing current would then act with greater force, and soon grind down a deep and capacious channel.

"[12] The original 'Lang Dyke' was constructed in 1773, later using stone from the Rashielee Quarry near Park Quay, finally resulting in the loss of the Dumbuck Ford and a great improvement in the navigation to Glasgow.

[15] In 1868 an oak dug-out canoe 22' (6.7m) in length and circa 2'10" (0.9m) was found near Milton Island containing deer horn, six stone axe heads and a possible paddle.