414 



W. TOPLEY AND G. A. LEBOUR ON THE INTRUSIVE 



Dykes Earm, about 4J miles south of Alnwick. Hence it can 

 be traced northwards, past Rugley, nearly to Alnwick, lying about 

 100 feet, or rather more, above the Hobberlaw Limestone, which is 

 the lowest good and thick limestone of the series in that district. 

 Here, too, the Whin has its lowest known position, as it lies nearly 

 1000 feet below the Great Limestone. The beds immediately above 

 the Whin are seen in a stream south-east of St. Margaret's Farm, 

 where they are much altered. 



Here we approach the country so well known to the late Mr. G. 

 Tate. The evidences of intrusion here are so abundant, and the 

 Whin has been so well described by Mr. Tate, that we need not 

 repeat the evidence in detail. From Ratcheugh northwards to 

 Dunstanborough the Whin lies in beds and bosses at various horizons, 

 but chiefly about the Great, Eight-yard, and Six-yard Limestones. 



At first one is disposed to believe that the Whin here lies more 

 irregularly than really is the case. But there are a great number 

 of faults separating the beds. Still there can be no question as to 

 the fact that the Whin breaks through the beds, and also that it 

 alters the rocks above it quite as much as it alters those below. 



The northern part of the county has been described by Sir W. C. 

 Trevelyan in the early paper already referred to. In Mr. Boyd's 

 paper many stratigraphical details are given, from which it appears 

 that the Whin west of Holy Island lies some 800 feet above the 

 Great Limestone, quite in the top beds of the Carboniferous-Lime- 

 stone series. In this district the Woodend Limestone (or the Hob- 

 berlaw Limestone) lies about 1000 feet below the Great Limestone. 



Now, on the south of Alnwick, near Rugley, the Whin lies about 

 100 feet above the Hobberlaw Limestone ; so that comparing the 

 two districts, we find that the Whin lies about 1700 feet higher in 

 the series near Holy Island than it does just south of Alnwick. 



At very numerous places along the outcrop of the Whin Sill 

 minor but equally good evidence of its non-contemporaneitj'' is forth- 

 coming. Among these the section at Shepherd's Gap (fig. 4) along 



Eig. 4. — Diagram Section from Shepherd's Gap eastwards. 



t? 



3L a HFile - 



a. Sandstone. 



b. Whin. 



c. Limestone. 



d. Shale. 



The Limestone seen lying upon the Whin in the eastern portion of the Sec- 

 tion is the same as the one shown lying beneath it in the western portion, and 

 being thrust into it. The beds lying above the Whin Sill are seen on the dip- 

 slope of the basaltic sheet at a lower level than the top of the escarpment ; it 

 has therefore been necessary to bring them out of their proper plane in order 

 to show them in the sketch. Although the upturned limestone is very clearly 

 shown in the face of the Crag, yet the disturbed beds associated with it are not 

 easily seen. This rearing limestone is all that Hutton shows. 



