26 
THE GEOLOGIST. 
at Bavington, and on the east coast at Dunstanburgh Castle, -^liere it 
forms a high escarpment facing the sea, and affords the very best oppor- 
tunity for observing tlie vertical columnar structure Tvhich it here assumes, 
with the usual lateral jointings. It again appears at Bamburgh Castle and 
the Farne Islands ; at the former, the columnar masses incline to an angle 
of forty-five degrees, as at Holy Island, w here it is again seen, and thence 
proceeds to the Kyloe hills, six miles northward from Belford. 
To account for the introduction of the whin sill into the limestone strata, 
two theories have been advanced. Mr. Huttou maintained that the Ba- 
saltic lava was poured out on the bed of the ocean, at one or more periods, 
during the deposition of the limestone strata, and thus became inter- 
stratified amongst them. Professor Sedgv\ ick, on the other hand, enter- 
tains the opinion that the eruptive lava, during a later period, forced its 
way into the previously deposited rocks, along their surfaces of stratifica- 
tion, and thus elevated the whole mass of superincumbent strata. 
Each hypothesis encounters its own peculiar difficulties vvliile endeavour- 
ing to account for all tlie phenomena. From his own observations of the 
wiiin sill, which have been confined to its more northern course, the Pre- 
sident was led to adopt, in preference, the hypothesis of Hutton. The 
force required to have horizontally opened and intruded so large a mass 
of igneous matter into the limestone beds for so many miles would be 
enormous, and was almost certain to have dislocated and greatly broken 
the superjacent strata, and to have intruded dykes and veins of Basalt in 
all directions into the adjacent fissures. Dislocations evidencing great 
violence in their production, and the intrusion of Basaltic masses, how- 
ever, are nowhere observable. Of the numerous faults that traverse the 
northern coal-field, two may be seen in our immediate neighbourhood, 
namely, the dyke in Tynemouth Cliff, and the ninety-fathom dyke near 
Cullercoats. The latter is of much geological interest, arising from the 
vast dislocations and remarkable downthrow of the strata it has effected 
along its whole uninterrupted course of one hundred and thirty miles. 
This great fault begins at the northern termination of the Pennine chain, 
and runs eastward to the sea-coast at Cullercoats, and has caused a relative 
depression x)f the limestone strata on the north, estimated at some points 
at not less than two thousand feet. Tiie depth of the downcast, however, 
varies much at different places : at Cullercoats it is nearly fifty fathoms. 
The fault can be best seen and studied at Cullercoats and Whitley, for 
here it has dislocated not only the coal-measures, but also the Lower Eed 
Sandstone and the magnesian limestone of the Permian series. The beds 
are invariably depressed on the north side, and dip towards the fault, the 
plane of the dislocation being about fifty-nine degrees. The surface of 
the overlying sandstone is marked along the dip of the fault by numerous 
parallel flutings made by the intruded mass, afi'ording the clearest evidence 
of the great violence with which the displacement was effected. The 
course of the dyke from Cullercoats to Gosforth is W.N.W., thence 
W.S.W. across the Tyne about three miles above Newcastle, and thence 
W. to Brampton, where it bends in a nearly S.E. by S. direction to 
Brough ; from Brough to Wild Boar Fell nearly S.W., and thence to 
Graygarth, S.S.W. ; from Gra3'garth to Wharfdale, E.S.E., turning a 
little more eastward as it approaches the Wharf. The geological age of 
this great igneous eruption seems pretty accurately indicated. It divides 
the lower Permian beds at Cullercoats, but does not appear to have dislo- 
cated the Triassic Eed Sandstones in its western course. It must, there- 
fore, have been intruded either about the time of the deposition of the 
middle, or of the upper, beds of the magnesian limestone — certainly not 
