The Wackerfield Dyke. 443 
sill must therefore closely approximate 1n position and form with the 
line we have drawn. The thickness of the sill could not be ascertained 
as the lower surface is nowhere exposed ; the deepest workings are 
filled with water, but a penetration into whinstone for at least 10 feet 
is certain. 
The rock from the dyke and from the upper part of the sill was 
much decomposed, particularly so in the latter case; in contact 
with the overlying sandstone and for a foot or more down it has 
been changed to a friable ochreous material easily mistakable at first 
sight for ferruginous sandstone. 
Exposure II.—The second exposure is found in a deeper quarry 
in an adjacent field, less than 100 yards N.E. from the first. The 
rock is almost completely hidden by debris and soil and consequently 
the cutting now gives very little information beyond fixing the 
direction of the dyke and indicating an approximate width. In 
Exposure I the dyke was striking nearly N.E.-S.W., in this it is 
running H.N.E.-W.S.W., a direction it continues to follow along the 
rest of its proved course. The estimated width must closely approach 
30 yards. What little rock was actually exposed was wholly 
dolerite, and this included some remarkably fresh material (6). The 
freshest samples were obtained near the surface immediately beneath 
a thin covering of drift. 
Fig. 2.—Section along A-B (Fig. 1), drawn from southern margin of dyke 
to middle of face “‘ 3°’. 
Exposure III.—This quarry, 250 yards east of Hilton Moor Farm, 
was “ opened out” within recent years, but has since been filled in 
again. Only a trench-like depression in the ground now marks the 
position and trend of the dyke, and affords data for a rough estima- 
tion of its width, which is evidently about 15 yards, No rock in situ 
can now be seen. 
Exposure IV.—The intrusion forms a well-marked feature where 
it enters Trunnelmire Plantation, but this*can only be followed 
a short distance into the wood. Three or four small trials made just 
within the plantation have exposed the rock; this is remarkably 
fresh. The dolerite forms here an outcrop at least 50 yards in 
width, and unless the dyke is abnormally wide at this point another 
sill is indicated. 
To summarize the information yielded by these exposures: The 
dyke can be traced for nearly a mile, and with the exception of 
a deflection near the western end it runs in a straight line; on the 
other hand it varies considerably in width, and is dilated at both 
