214 Prof. Sedgwick on some Trap Dykes 
sionally appear among the newest secondary rocks. The facts 
exhibited by the north coast of Ireland have been already al- 
luded to. ‘The great dyke which starting from Cockfield Fell, 
in the county of Durham, crosses the plain of Cleveland, and 
terminates in the eastern moors of Yorkshire, leads us to a si- 
milar conclusion. 
Cockfield Fell and Cleveland Dykes. 
This dyke, which preserves such an extraordinary continuity, 
forms a striking feature in all the geological maps of the di- 
strict. Some good general descriptions have already been 
given of it*. My principal object in this paper will be, to 
place before the Society, in a connected point of view, those 
facts which appear to bear on the question of its origin. I shall 
afterwards notice some pheenomena which are exhibited in High 
Teesdale, and seem to throw light on the same question. 
Dykes near Egglestone in Upper Teesdale. 
A mass of trap occupies the lower part of the left bank of 
the river Tees exactly opposite to the entrance of the Lune. 
It may be traced without difficulty for three or four hundred 
feet, close to the edge of the water; and it at length disap-~ 
pears under Egelestone bank; where it rests upon, or abuts 
against a bed of slate clay. The prolongation of the trap to 
the other side of the Tees is rendered highly probable by the 
appearance of a bed of similar character in the left bank of the 
Lune immediately under Lonton Chapel. But the accumu- 
lation of diluvium prevents this connexion from being esta- 
blished by direct evidence. The imperfect denudation on the 
left bank of the Tees did not allow me to ascertain the exact 
relation which the trap on that side of the water has to the 
contiguous strata. Above Egglestone bank another mass of 
trap, to all appearance immediately connected with that which 
has been described, crosses the road about a mile to the north- 
west of the village. It there assumes the unequivocal charac- 
ters of a dyke, ranges (as nearly as I could discover from very 
imperfect data) E. by N. and a few hundred yards above the 
road crosses the western branch of the rivulet which runs past 
Egelestone. A quarter of a mile further up the same branch 
of the rivulet, a second dyke crosses its bed, and seems to 
range about S.E. by S. From what has been stated it appears 
probable that these two dykes unite, or intersect each other. 
Their concourse will probably be found on the moor above 
the new smelting-house. ‘The former, where it is seen above 
* Geological Survey of the Yorkshire Coast, by Young and Bird. p. 17]. 
Egglestone, 
