Parliamentary plans on these lines approved of by James Walker, Consulting Engineer to the Trustees, were submitted to and sanctioned by Parliament in 1840; but so inadequate was the appreciation of the depth required, that 20 ft. at high water neap tides was recommended by Logan as the extreme depth of the river and harbour, and a clause in the Act empowering the deepening to proceed until every part thereof shall have attained at least a depth of 17 ft. at high water neap tides. The depth in the harbour of Glasgow at the present time is from 25 ft. to 29 ft, and in the river from 27 ft. to 29 ft. at high water neaps, high water springs being about 2 ft. higher. The average tidal range of spring tides at Glasgow is 11 ft. 2 in., and at Port Glasgow 10 ft.; and of neaps at Glasgow 9 ft. 2 in., and at Port Glasgow 8 ft. 3 in. While jetties and training walls, or parallel dykes, performed a useful part in the early improvement of the river, it is to persistent dredging that the enormous increase in the magnitude of the river since 1840 is due. The early dredging was performed by large rakes, or porcupine ploughs, as they were called, because they were provided with strong iron teeth, wrought by hand capstans, which drew the material from the bed of the river on to the banks. Hand-wrought, and subsequently horse-wrought, dredges, with small buckets on a ladder, succeeded the plough, and in 1824 the first steam dredger was started on the river. It dredged, however, only to 10 ft 6 in. Now several of the dredges employed can work in 35 ft. depth of water. Mr. Deas, the engineer to the Clyde Trust, has stated[55] that it is due to the application of steam power to dredges, and the subsequent adoption of steam hopper barges for carrying the dredged material to the sea, that the rapid enlargement not only of the Clyde and the Harbour of Glasgow, but of the Tyne, the Tees, and several other similar rivers in recent years are due. But for the introduction of the latter, it would have been physically, financially, and otherwise impossible to have disposed, within so limited a time, of the enormous quantities of material which have been dredged from these various rivers and harbours.