108 REPORT— 1859. 



On some Basaltic Formations in Northumberland. 

 By William Sydney Gibson, M.A., F.S.A., F.G.S. 



The basaltic formations in Northumberland not only contribute to the picturesque 

 outline and the wildness of much of its scenery, but present some remarkable 

 features in their structure and in the manner of their association with other rocks. 



A range of basalt traverses the county from south-west to north-east, in a ridge 

 or belt of varying and often considerable height, but inconsiderable breadth, 

 entering Northumberland near the Cumbrian border. This ridge first begins in 

 the dale or "forest" of the Lime, and sweeps round the great western escarpment 

 of the limestone ranges of Cross-Fell and Tynedale-Fell ; then, curving towards 

 Thirlwall on the border of Cumberland, it runs from thence north-eastward with 

 bold escarpments towards the north, and crossing the North Tyne, extends to the 

 sea-coast at Howick ; it then rises at Bamburgh, and after a tortuous course to the 

 north-west, ends in the low range of hills called the Kyloe Crags. The rocky 

 group or "seventeen sister-satellites" of Fame are a seaward prolongation of the 

 great basaltic range. Basaltic veins or dykes also run towards the coast of the 

 county (as at Holy Island, Beadnell, andTynemouth), and seem to have a direc- 

 tion transverse to the great ridge. 



In the western part of the county, the basaltic crags are associated with that 

 wonderful monument of Roman occupation — the Great Wall, its builders having 

 availed themselves of the precipitous ridges, and carried the wall above many a 

 bold escarpment of basaltic rock. A crest of this formation near Wall-town, which 

 was formerly crowned by a Roman Mile-Castle of the Wall, is 800 feet above the 

 sea-level ; and at a Roman camp to the westward, known as Sewingsheles, the 

 summit attains the height of 960 feet. In this wild district, once adjacent to 

 populous Roman Stations, but where now only the moor-fowl dwells among the 

 heather of neighbouring wastes, are the lonely sheets of water known as the 

 Northumberland Lakes, one of which, called Crag Lough, lies at the foot of the 

 basaltic cliffs. 



In the northern part of the county the basalt likewise forms rocky masses of 

 considerable height, often precipitous on their western side, and culminating at one 

 place at 570 feet above the level of the sea. Many of these eminences have been 

 chosen for the site of Castles, as at Bamburgh, Holy Island and Dunstanburgh, 

 where the caverned rocks of columnar basalt rise 100 feet above the surging 

 waves. At Bamburgh (an important citadel from days of Saxon royalty) the 

 draw-well of the fortress has been sunk through 75 feet of basaltic rock, and 

 through a like thickness of the fine-grained reddish tinted sandstone on which it 

 rests. On the rocky islets of Fame the basalt even exceeds this thickness. 



The isolated, metamorphic and dislocated condition of the beds of sandstone, 

 limestone, and shale on some of the Fame islands, seems to indicate that the 

 basalt flowed in its igneous state over these lower groups of the limestone series. 

 On the coast at Howick, a little to the south, the basalt appears in the form of 

 dykes which intersect the cliffs of carboniferous limestone, shale and sandstone. 

 A formation of basalt, which seems to have overflowed after the deposit of this 

 group, overlies it. Elsewhere in Northumberland a stratiform basalt is found 

 associated with the carboniferous rocks, and in some localities is interstratified 

 with them ; thus, a bold columnar cliff called Ratcheugh Crag, near Alnwick, one 

 of the range of basaltic eminences which run inland from the coast at Dunstan- 

 burgh, is capped with the carboniferous limestone. Another basaltic eminence 

 between Alnwick and the coast rests on beds of blue limestone and nietamorphic 

 shales, which in some localities Mr. George Tate of Alnwick, F.G.S., a diligent and 

 able naturalist, found to have been converted into a porcelain jasper, and where 

 in direct contact with the basalt, into a black mineral of conchoidal fracture. At 

 Ratcheugh some of the limestones above the basalt have been changed into granular 

 marble. 



In some localities of this carboniferous limestone district, as at Howick and 

 Bamburgh and on the Fame, the rocks have been disturbed by an eruption of 

 basalt ; and it occurs both as an injected dyke and an overflowing lava, and seems 

 to indicate successive volcanic outbursts during as well as subsequent to the era 

 of those formations. 



