Geology of High Teesdale. 145 
Among the circumstances of most importance in the struc- 
ture of High Teesdale, appear to be the following: 
(1.) The want of correspondence in the strata, on the two 
sides of all that part of the valley, which extends five or six 
miles above Eglestone. 
(2.) The manner in which masses of trap are, in this part 
of the valley, associated with the other strata; more especially 
the appearance of a great bed of trap (the great Whin-Sill of 
the mining district) first on the south side of the valley, and 
afterwards in the banks, and in the bed of the river. 
(3.) The appearance of a great transverse faulé, which inter- 
sects the whole valley about a mile above the High Force (in 
a direction which is about N.N.W. and E.S.E.), and throws 
the whole system of strata on the south-west side of its range, 
twenty or thirty fathoms above their natural level: thus ex- 
hibiting in the highest part of Teesdale, a repetition of the phe- 
nomena which appear at the junction of the trap with the 
other strata. J 
I. To these facts I now proceed to call the attention of the General se-- 
Society, in the order just pointed out. In the hope of making oe 
these complex phenomena better understood, I shall subjoin 
a detailed section of the strata in High Teesdale; and shall add 
a section of the upper beds of the same series, obtained from 
the lead-works of Old Langdon, in the High Moors, which 
extend to the north-west of Middleton. 
Vol. II. Part I. T 
