Geology of High Teesdale. 169 
I now proceed to consider the effects apparently produced 
by its contact with the other strata. These effects are of two 
kinds—mechanical and chemical. By mechanical effects, are 
understood an alteration in the position of certain beds, or the 
parts of certain beds, by the agency of the trap: by chemical 
effects, are understood, some changes produced by it in the tex- 
ture and mineralogical character of the contiguous rocks. 
1. To the mechanical action exerted by the trap, I venture 
to attribute the shattered appearance of the strata on the 
crest of the hill above the new plantations north of Eglestone. 
It was this very appearance, seen from the opposite side of the 
valley, which first led me to suspect, that the upper dyke passed 
considerably to the north of the direction which I had given it in 
my former Paper (supra, p. 25.) A subsequent examination 
confirmed this suspicion, and enabled me to ascertain, that the 
upper dyke (see the Map, PI. vir.) ranges through the center of 
the shattered beds which belong to the mdl-stone grit (general 
Section, No. 1,) and that it has apparently protruded some masses 
of slate-clay from their true situation. These masses of slate-clay 
are ina state of considerable induration ; but it is not clear that 
their present state is to be ascribed to any direct agency of the 
trap dyke. 
2. By the operation of similar causes, we may readily account 
for the extraordinary appearance of the strata near Greengate- 
farm, in Lunedale, (See the Map, Pl. vii.) The beds of limestone 
and sandstone, unquestionably belong to the general Teesdale 
section, but they are broken and tilted in every possible direction, 
(See the Section, Pl. vit. Fig. 3.) Had the trap been regularly 
deposited along with the other strata, I cannot conceive any 
system of disturbing forces capable of producing the present ar- 
rangement. If, on the contrary, we suppose it to have been 
forcibly driven up amongst the other beds after their partial con- 
Vol. MI. Part I. Y 
Effects pro- 
duced by the 
Trap. 
Eglestone 
urn. 
Effects of the 
Trap in Lune- 
dale. 
