"The parish of Allendale is, strictly speaking, a parochial chapelry of the ancient parish of Hexham, and is only divided from it by a series of artificial lines drawn through the old Hexham and Allendale common. It is bounded on the south by the counties of Durham and Cumberland, and on the west and north by the parish of Whitfield and the chapelry of Haydon Bridge. Its fells and moors, high, bleak, and bare, but rich in minerals, are broken by many water-worn hollows, the local cleughs, and by two great parallel valleys, through which flow the two rivers of East and West Allen. Both of these streams take their rise on the confines of Northumberland and Durham in the same watershed, whence the Wear and the South Tyne have their origin. In their course they form many 'beautiful bays and peninsulas, boundered by rocks and hanging woods, affording a multitude of little solemn and secluded retreats through which the waters murmur." After receiving numerous smaller streams, such as Acton burn, Crockton burn, Knockshield burn, Mohope burn, Oakey-dean burn, Steel burn, Sinderhope burn, Swinhope burn, and Whitewalls burn, they unite below Hindly Wrae and form the Allen, which has cut its way through narrow and precipitous gorges near Staward, and enters the Tyne at Ridleyhall. From these two streams is derived the distinctive name of the district, the termination of the name being common to Tynedale, and many other parts of Northumberland. The population which, owing to the failure of the lead trade, has rapidly declined, has always been gathered together in the two valleys."
A History of Northumberland: Vol IV - John Crawford Hodgson 1897