The Wackerfield Dyke. 441 
The field investigation has been carried out by one of us [S.8.] 
and the petrological study by the other [A.H.], and a very complete 
analysis of the rock has been contributed by Dr. H. F. Harwood. 
Field Relations: Situation: 1 inch Geological Map 102 8.W. 
(New Series Sheet 32), 6 inch map Durham Quarter Sheets 47 N.E. 
and 48 N.W. Latitude (approx.) 54° 36’; longitude 1° 451° 46’. 
The dyke runs E.N.E—W.S.W. and can be followed for 1,700 
yards, from an old quarry a quarter of a mile north-east of Wackerfield 
(a hamlet 2 miles north-east of Staindrop) to the edge of Trunnelmire 
Plantation. It outcrops on the divide between the Tees and the 
Gaunless, a tributary of the Wear, and itself forms the axis of 
a ridge. 
Description of Outcrop.—The dyke has been exposed by quarrying 
at four places, and it will be convenient to give a brief description 
of each of these with a view to outlining the general habit of the 
intrusion. We have indicated these exposures on the sketch-map 
of the dyke (Fig. 1) by Roman numerals, and have utilized 
Arabic figures to serve as further points of reference. These Arabic 
figures also denote the places from which rock specimens were 
collected. 
Exposure I—The most westerly exposure is an old quarry near 
the road ; this is the best and at the same time the most interesting 
exposure along the line of the dyke, despite the fact that the old 
workings are now much obscured by debris and are overgrown by 
vegetation. The total length of the excavation is about 150 yards, 
but this includes both a whinstone and a sandstone quarry separated 
by a thin partition of unworked rock. The dyke runs along the south 
side of the two quarries and is here very narrow, at the point 2 
where both “cheeks” were exposed by hammering its width was 
rather less than 8 yards. It spreads laterally, however, to form a sill 
to the north. The limits of the sill cannot be proved ; the apophysis 
extends along the dyke for at least 60 yards, and is exposed about 
the same distance to the north of it (point 5). The surface features 
indicate an extension of the sill for some yards north and west of the 
quarries, but neither the dyke nor the sill have been proved west 
of the actual whinstone excavations. With fissile sandstone over- 
lying it the sill is well exposed on the east side of the whinstone 
quarry, indicated at 3 in the remnant of unworked stone that 
divides it from the sandstone workings. This face of rock runs 
almost at right angles to the dyke. The upper surface of the sill 
as seen in this face is practically horizontal and fairly regular, but it 
rises to the west and reaches the surface of the ground within a few 
yards. 
Although very little solid rock could be laid bare in the shallow 
workings between the exposure described and a deep excavation in 
sandstone at the point marked 4, such rock as could be exposed 
was wholly sandstone. The north cheek of the dyke was proved in 
the south side of this deep excavation, and the eastern limit of the 
