20 



THE GEOLOGIST. 



at Bavington, and on the east coast at Dunstanburgh Castle, where it 

 forms a high escarpment facing the sea, and affords the very best oppor- 

 tunity for observing the vertical columnar structure which it here assumes, 

 with the usual lateral jointings. It again appears at Bamburgh Castle and 

 the Fame Islands ; at the former, the columnar masses incline to an angle 

 of forty-five degrees, as at Holy Island, where 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. Hutton 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 Sedgwick, 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 while endeavour- 

 ing to account for all the phenomena. From his own observations of the 

 whin 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 of the limestone strata on the north, estimated at some points 

 at not less than two thousand feet. The 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 Red 

 Sandstone and the magnesiau 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, affording 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 

 Gray garth, S.S.W. ; from Graygarth 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 Bed 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 magnesiau limestone — certainly not 



