152 Reginald A. Daly — 



This area is dangerous for climbers. Its slopes tend to become 

 veneered with, a coat of creeping, tuff-like mud, which greatly 

 obscures details. Hence a complete study of the dikes is a very 

 slow, if not impossible task. At several points, however, it was seen 

 that the intrusions form most unusual examples of multiple dikes. 

 As many as twenty contact directly with each other in succession, 

 without any intervening tuff or other material. So crowded are they 

 in the middle of the ridge joining Flagstaff Hill and The Barn that 

 some 200 of the sheets of rock seem to constitute one gigantic 

 multiple dike. In the writer's experience this part of the complex 

 is quite peerless for the number of distinct, basaltic intrusions 

 outcropping in so small a space. The nearest parallels to such 

 persistence of igneous injection are perhaps the belts of " inclined 

 sheets " in the Scottish islands of Mull and Skye, though the causes 

 of tension and injection may be essentially different. 



Other dikes of the Knotty Eidge complex, having trends unlike 

 those of the two principal systems, and combined with the latter, 

 constitute dike networks of unmappable complication. 



From the lips of many of the Knotty Ridge fissures, and presumably 

 from others not yet exposed by erosion, lava-flows were poured out. 

 The result was a high, exogenous, basaltic dome, which centred 

 nearly under Deadwood Plain. From that general centre the thin 

 flows ran on slopes that decreased from 25° to 10°, as far as James- 

 town on the north-west and Sane Valley on the south-west. Flagstafi 

 Hill and The Barn are erosion-remnants of this thick capping of many 

 flows, which formerly covered the whole of the visible Knotty Ridge 

 complex as well as its continuation in Flagstaff Bay. 



No volcanic neck is exposed, and, as throughout the island in 

 general, the growth of the north-eastern end of St. Helena was due 

 to fissue-eruption rather than to eruption from local, persistent 

 vents of the central type. Scores of dikes cut the capping flows of 

 Flagstaff Plill and The Barn. The flows are massive and strong ; 

 the complex is remarkably weak and friable. Hence have been 

 conditioned some of the finest canyon-like scarps and sea-cliffs in 

 the island. 



A very similar complex covers nearly 3 square miles in the 

 lower part of the basin comprising the Sandy Bay district. In the 

 writer's opinion, this huge cirque is neither a crater nor a caldera, 

 but owes its imitative shape to erosion, working on a special structure. 

 Erosion was bound to begin the widening-out of just such an 

 amphitheatre as soon as the weak rocks of the underlying complex 

 in their actual distribution were uncovered. 



Hundreds of dikes of the Sandy Bay Complex, including many 

 dikes, generally run parallel, in a north-east — south-west 

 direction, on which some of them keep for nearly 3 miles. Dikes 

 of similar trend were found far to the north-eastward of the Sandy 

 Bay district. As near Deadwood, the dike fissures here were vents 

 through which many lava-floods were emitted. The lavas ran in all 



