X. On the Association of Trap Rocks with the Mountain 
Limestone Formation in High Teesdale, &c. 
By tue Rey. A. SEDGWICK, M.A. F.R.S. & M.G.S. 
WOODWARDIAN PROFESSOR, AND FELLOW OF TRINITY COLLEGE, 
{Read May 12, 1823; March 1, and March 15, 1824.] 
Section [. 
On the great Calcareous Chain of the North of England. 
In a paper which was read to the Society last year*, [ Trap of High 
described some of the principal phenomena exhibited by the ia 
great dykes of Cockfield Fell and Cleveland. I also brought 
forward some facts which made it probable, that either the 
dykes above-mentioned, or other masses similarly associated 
with the coal formation, were prolonged into High Teesdale, 
and connected with the beds of trap which form so extraor- 
dinary a feature in that region. 
Having concluded, on evidence which seemed quite irre- 
sistible, that this intrusive class of rocks was of igneous origin, 
it became the more necessary to examine the trap of High Tees- 
dale, provincially termed the great Whin Sill +: especially since 
* The paper alluded to is printed in this Volume, p. 21, &e. 
+ The word Sill, is, in some of the mining districts of the north of England, 
synonymous with stratum. By the Whin Sill is, therefore, understood a large tabular 
mass of trap imbedded in, and nearly parallel to, the other strata. 
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