The Shannon river forms the most important feature in the inland navigation of Ireland. For the first 144 miles of this waterway, from the head of Lough Allen to the sea below Limerick, the Shannon is like a series of rivers and lakes. Issuing from Lough Allen, it passes Leitrim, Carrick, Tarmonbury, &c., and then enters, at Lanesborough, a very irregularly-shaped and extensive sheet of water, called Lough Ree, about 17 miles in length. Leaving it, the river, now greatly augmented, passes Athlone, and then winds by Shannon Bridge and Banagher to Portumna, near which it expands into Lough Derg, another narrow lake, 23 miles long, with deep bays and inlets. From the southern extremity of this lake it flows on to Limerick. In this extent of navigation we have first Lough Allen, 10 miles; thence to Lough Ree, 43; Lough Ree itself, 17; thence to Lough Derg, 36; Lough Derg, 23; thence to Limerick, 15; making together 144 miles. The mean height of Lough Allen above the sea at Limerick is about 143½ feet, being on an average about a foot of declivity per mile. Instead of the natural fall, however, the water has been reduced by means of locks to a series of level pools. The estuary or firth of the Shannon extends south-west about 70 miles beyond Limerick to its mouth, which is finally about 8 miles wide between Loop Head and Kerry Head, at the Atlantic. The direction of the Shannon from Lough Allen to Limerick, though generally south by south-west, is very circuitous, and broken by many streams, islands, and rocks. The soundings are as various, and both banks are liable to be overflowed by the river to a great extent; and the large expanse of the lakes would require a different sort of vessel from those which navigate the river. The works which have been constructed to overcome the natural difficulties of the navigation are either insufficient or in a state of decay; and it seems to be generally admitted that very little real good can be effected until the natural obstructions are removed, the number of lakes reduced, and the channel deepened and improved in various parts; though it is still doubted if the navigation would even then be suitable for anything but steam-vessels. The Shannon connects with the Royal Canal at Tarmonbury, and with the Grand Canal at Shannon harbour, near Banagher. At Shannon Bridge it receives on the west its principal tributary, the Suck; on the east, the Inny, the Upper and Lower Brosna, Mulkerna, Maig, Fergus, &c. The Shannon river connects the tide water of the Atlantic in Limerick with Dublin by two canals, the Grand and the Royal. It passes by the towns of Limerick, Killaloe, Portumna, Banagher, Shannon Bridge, Athlone, Lanesboro’, Yarmon, Roosky, Drumsna, Carrick, Leitrim, and Drumshambo.