Dislocations in 
Tamedale. 
150 Professor Sepawick on the 
lower part of Lunedale. This want of agreement in the cor- 
responding parts of the same formation is not accounted for by 
their direction and their dip; but is supposed to originate in a 
longitudinal fault, (the great Teesdale fault) which commences 
near Eglestone Bridge, and throws the whole system of strata on 
the north side of the valley below their original level. This fault 
is not interposed hypothetically for the mere purpose of meeting 
the difficulty ; for we have direct evidence for its existence in the 
bed of the river above Eglestene Bridge, and in the right bank of 
the Lune very near its junction with the Tees. Between these two 
places, the line of fault passes on the south side of the Tees 
through the low grounds under the village of Mickleton*. 
Before I proceed to trace the progress of this fault farther up 
Teesdale, it may be proper to remark, that im many of the 
lower parts of Lunedale, more especially on the west side of 
the rivulet near Greengate and Saddle Bow, the strata are in a 
state of inextricable confusion. The whole country appears to be 
externally modified by disturbing forces, which have rent asunder 
the beds of rock and heaved them entirely out of their natural 
position and inclination. From this part of the valley of the 
Lune, a great break in the strata ranges towards Teesdale, and 
* In the mining districts of Durham, every species of nearly vertical fissure, by which the 
continuity of the strata has been interrupted, is called a vein. The corresponding beds, on the 
opposite sides of these fissures, are very seldom on the same level; and the interval is sometimes 
filled up with materials (provincially called riders) which are highly metalliferous. 
In some parts of the Lodge Syke vein, which is worked in the hill immediately north of 
Middleton, the rider is not less than twenty-four feet wide. It consists of shattered fragments 
of the neighbouring strata mixed with oxide of iron; the whole being cemented and held 
together by quartz, fluor-spar, carbonate of lime, and great ribs of galena. 
But there are many dislocations in the district where the rider is altogether of a different 
character. The masses on opposite sides of the fracture are in some places in almost imme- 
diate contact, in other places they are separated from each other by thin beds with an imperfect 
vertical cleavage, which were probably formed at the time of the fracture by the motion of 
the broken edges past each other. It is from indications of this kind that the great Teesdale 
fault has been traced in the bed of the river near Eglestone. 
ie a 
