87 
This diversion of rivers by glacial action is referred to by 
Geikie, in his “Great Ice Age/’ but the Wear gives better 
instances than I imagine can elsewhere be found. 
Above Durham the river meanders through a valley 
resembling that of the Irwell opposite Kersal-moor, one or 
both of the opposite banks being composed of drift. At 
Durham itself a firm dam of clay has been thrown across 
the old valley, and the river has cut a narrow horseshoe- 
shaped ravine in the solid rock, thus isolating the block of 
stone on which the cathedral and castle stand. As soon as 
the stream emerges again from the rock into the pre-glacial 
valley, the bounding cliffs fall back, and the valley widens 
below as above the town. The narrow isthmus which joins 
the isolated block of rock is called Clay-path, and the 
boulder-clay in it is decidedly tough. 
There are other instances of this clay-bar across the old 
river valley, and the isolation of a block of rock connected 
with the opposite side by a clay mound which has usually 
by this time weathered much lower than the isolated rock 
above which at first it must have risen. There is a very 
beautiful examp] e of this (one amongst many) on the Esk, 
by Lealholm Station, near Whitby. 
At Sunderland Bridge Station on the N.E.R. mainline to 
the south of Durham is one of these diverted channels, half 
cut down. The river has begun a semi-circular ravine in 
the solid rock, but after it had dug down some 40 feet the 
clay barrier failed, and the ravine is left apparently pur- 
poseless. The Sunderland-bridge Kailway Station stands in 
the hollow, and the railway forms the sagitta, whilst the 
viaduct across the present valley of the Wear beyond marks 
the site of the former clay barrier. Narrow, rocky-sided, 
and deserted river valleys will therefore be usually of post- 
glacial formations. 
This Wash, or old valley of the Wear, proves that before 
the glacial period the north-eastern part of England was at 
