The area covered by this paper embraces the northern end of the Pennines—the uplands of Lower Carboniferous rocks centred about Alston, together with the low ground of the Tyne-Irthing gap to the north. It is bounded on the west by the Vale of Eden. The Pennine portion is separated structurally from the regions to the north and west by the Stublick and Pennine Faults respectively. The former trends E.N.E., it has a downthrow to the north and has resulted in the preservation of the string of Coal Measures outliers which form a connecting link between the Cumberland and Northumberland coalfields. The Pennine Fault, trending S.S.E., with a throw of several thousand feet to the west, brings the New Red rocks of the Vale of Eden against the Lower Carboniferous beds of the Pennine Escarpment. These two faults meet at right angles near Castle Carrock. To the south the Pennine Fault dies out near Stainmore, and another dislocation, the Dent Fault, trending S.S.W., develops, and eventually links up with the Craven Faults which have an E.S.E. trend. These four faults, as pointed out by Professor Kendall, have the form of a reversed 3, and the region within this figure has become known generally as the Northumbrian Fault Block. Professor Marr has aptly termed the southern half of this area the “Rigid Block”. The northern half of the Northumbrian Fault Block, which will be shown to possess many characters in common with the southern half, is here called the “Aiston Block”. Its limits are defined on three sides—by the Stublick Fault on the north, the Pennine Fault on the west, and by the Stainmore depression on the south. The last thus divides the Northumbrian Fault Block into two, physiographically and structurally. The eastern boundary of the Alston Block is concealed beneath the Mesozoic rocks.