42 Professor Sepawick on Trap Dykes 
(5). The dyke appears to decrease in width as it rises towards 
the surface. Thus, in Crowtrees colliery, the width of the dyke, 
where it is cut through at the depth of fifteen fathoms, is nearly 
twice as great as at the surface. 
(6) It does not appear at Quarrington Hill to cut through 
a bed of sand and pebbles, which lies between the highest beds 
of the coal-formation and the magnesian limestone. 
The importance of these facts in confirming the theoretical 
views given in the preceding paper, is too obvious to need any 
explanation. 
Mr. Winch asserts (Geological Transactions, vol. IV. p. 25.) 
‘* that he has never been able to trace any of these basaltic veins 
‘into the magnesian limestone, and is almost certain that, with 
‘other members of the coal-formation, they are covered by it.” 
The dyke just described affords some additional evidence in 
support of this opinion. Moreover, it appears, in its general 
relations, to agree so exactly with the Cocktield Fell dyke; that 
I now cannot help suspecting, that this latter also belongs to the 
class of ‘* basaltic veins” which do not pass up into the magnesian 
limestone, though I inclined to a different opinion when the pre- 
ceding paper was written. 
Respecting the prolongation of the Cockfield Fell dyke 
through the region of the magnesian limestone, there are con- 
flicting probabilities which lead to directly opposite conclusions. 
The near agreement in the direction and dip of the Cockfield 
Fell and Cleveland dykes, has generally been supposed to afford 
sufficient evidence for their continuity. If this opinion be adopted, 
we must, I think, be compelled to admit the existence of a dyke 
through all the imtermediate district*.—On the contrary, there 
is no direct evidence for the existence of any trap associated with 
*% 
See the observations at p. 29 of this paper, 
